Performance of creatinine- or cystatin C–based equations to estimate glomerular filtration rate in sub-Saharan African populations

Predictive effect of estimated glomerular filtrate rate by creatinine or cystatin C on mortality in patients with coronary artery disease

BACKGROUND

Renal dysfunction leads to poor prognosis of patients with coronary artery disease (CAD). Current studies have reported the prognosis or mortality of various diseases using different estimated glomerular filtrate rate (eGFR) formulas, while the performance of these equations is unclear in CAD patients. We aim to evaluate the predict effect of creatinine-based eGFR (eGFRcr), cystatin C-based eGFR (eGFRcys), and both creatinine and cystatin C-based eGFR (eGFRcr-cys) in CAD patients.

METHODS

A total of 23,178 patients with CAD were included from CIN-II cohort study. The association of eGFRcr, eGFRcys and eGFRcr-cys with cardiovascular and all-cause mortality was detected by Cox regression analysis. The predictive effect of eGFRcr, eGFRcys and eGFRcr-cys on mortality was assessed.

RESULTS

During a median follow up of 4.3 years, totally 2051 patients (8.8%) experience all-cause mortality, of which 1427 patients (6.2%) died of cardiovascular disease. For the detection of cardiovascular mortality among CAD patients, eGFRcr-cys had high discriminatory capacity with area under the curve (AUC) in receiver operator characteristic analysis of 0.730, which was significantly better than eGFRcr (AUC = 0.707, p < 0.001) and eGFRcys (AUC = 0.719, p < 0.001). Similar results were observed in all-cause mortality. Restricted cubic spline showed a U-shaped association between eGFRcr and all outcomes in patients with both reduced and supranormal eGFR levels, while a L-shaped association in eGFRcys and eGFRcr-cys.

CONCLUSIONS

Estimated GFR based on both creatinine and cystatin C has highest predictive effect for cardiovascular and all-cause mortality among CAD patients. Meanwhile, supranormal eGFRcr may indicate a higher risk of mortality.

Assessing bias in GFR estimating equations: improper GFR stratification can yield misleading results

BACKGROUND

Assessing bias (estimated - measured) is key to evaluating glomerular filtration rate (GFR). Stratification by subgroups can indicate where equations perform differently. However, there is a fallacy in the assessment of two instruments (e.g., eGFR and mGFR) when stratifying on the level of only one of those instruments. Here, we present statistical aspects of the problem and a solution for GFR stratification along with an empirical investigation using data from the CKiD study.

METHODS

Compared and contrasted biases (eGFR relative to mGFR) with 95% confidence intervals within strata of mGFR only, eGFR only, and the average of mGFR and eGFR using data from the Chronic Kidney Disease in Children (CKiD) study.

RESULTS

A total of 304 participants contributed 843 GFR studies with a mean mGFR of 48.46 (SD = 22.72) and mean eGFR of 48.67 (SD = 22.32) and correlation of 0.904. Despite strong agreement, eGFR significantly overestimated mGFR when mGFR < 30 (+ 6.2%; 95%CI + 2.9%, + 9.7%) and significantly underestimated when mGFR > 90 (-12.2%; 95%CI - 17.3%, - 7.0%). Significant biases in opposite direction were present when stratifying by eGFR only. In contrast, when stratifying by the average of eGFR and mGFR, biases were not significant (+ 1.3% and - 1.0%, respectively) congruent with strong agreement.

CONCLUSIONS

Stratifying by either mGFR or eGFR only to assess eGFR biases is ubiquitous but can lead to inappropriate inference due to intrinsic statistical issues that we characterize and empirically illustrate using data from the CKiD study. Using the average of eGFR and mGFR is recommended for valid inferences in evaluations of eGFR biases.

Which is the best glomerular filtration marker: Creatinine, cystatin C or both?

BACKGROUND

The glomerular filtration rate (GFR) is estimated by the serum or plasma concentration of creatinine and/or cystatin C using equations that include demographic data. The equations worldwide most widely used are those of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) consortium and updated in 2021 to remove the Afro-American racial correction factor. In 2021 and then in 2023, the European Kidney Function Consortium also developed equations based on creatinine and cystatin C, usable across the full age spectrum, and constructed by including the Q value (i.e. the median creatinine or cystatin C in healthy men and women, which is customizable for specific populations).

METHODS

The aim of this narrative review is to examine the strengths and weaknesses of each biomarker.

RESULTS

Both biomarkers have non-GFR determinants, namely muscle mass, protein intake and tubular secretion for creatinine; dysthyroidism and systemic corticosteroids for cystatin C, as well as other more debated determinants (diabetes, obesity, proteinuria, inflammatory syndrome). These non-GFR determinants are the reason why no equation based on a single endogenous biomarker has an accuracy within 30% greater than 90% over the entire age spectrum (in at least one patient in 10, estimated GFR is at least 30% higher or at least 30% lower than the measured GFR).

CONCLUSION

Equations combining the two biomarkers provide a better estimate of GFR, particularly in the subgroup of patients whose estimates based on each of the biomarkers are highly discordant. These patients must also be identified as being at increased risk of morbidity, particularly cardiovascular, and mortality.

Diagnostic standard: assessing glomerular filtration rate

Creatinine-based estimated glomerular filtration rate (eGFR) is imprecise at individual level, due to non-GFR-related serum creatinine determinants, including atypical muscle mass. Cystatin C has the advantage of being independent of muscle mass, a feature that led to the development of race- and sex-free equations. Yet, cystatin C-based equations do not perform better than creatinine-based equations for estimating GFR unless both variables are included together. The new race-free Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation had slight opposite biases between Black and non-Black subjects in the USA, but has poorer performance than that the previous version in European populations. The European Kidney Function Consortium (EKFC) equation developed in 2021 can be used in both children and adults, is more accurate in young and old adults, and is applicable to non-white European populations, by rescaling the Q factor, i.e. population median creatinine, in a potentially universal way. A sex- and race-free cystatin C-based EKFC, with the same mathematical design, has also be defined. New developments in the field of GFR estimation would be standardization of cystatin C assays, development of creatinine-based eGFR equations that incorporate muscle mass data, implementation of new endogenous biomarkers and the use of artificial intelligence. Standardization of different GFR measurement methods would also be a future challenge, as well as new technologies for measuring GFR. Future research is also needed into discrepancies between cystatin C and creatinine, which is associated with high risk of adverse events: we need to standardize the definition of discrepancy and understand its determinants.

Accuracy of GFR estimating equations based on creatinine, cystatin C or both in routine care

BACKGROUND

New equations to estimate glomerular filtration rate based on creatinine (eGFRcr), cystatin C (eGFRcys) or both (eGFRcr-cys) have been developed by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the European Kidney Function Consortium (EKFC). There is a need to evaluate the performance of these equations in diverse European settings to inform implementation decisions, especially among people with key comorbid conditions.

METHODS

We performed a cross-sectional study including 6174 adults referred for single-point plasma clearance of iohexol in Stockholm, Sweden, with 9579 concurrent measurements of creatinine and cystatin C. We assessed the performance of the CKD-EPI 2009/2012/2021, EKFC 2021/2023, revised Lund-Malmö (RLM) 2011 and Caucasian, Asian, Pediatric and Adult (CAPA) 2014 equations against measured GFR (mGFR).

RESULTS

Mean age was 56 years, median mGFR was 62 mL/min/1.73 m2 and 40% were female. Comorbid conditions were common: cardiovascular disease (30%), liver disease (28%), diabetes (26%) and cancer (26%). All eGFRcr-cys equations had small bias and P30 (the percentage of estimated values within 30% of mGFR) close to 90%, and performed better than eGFRcr or eGFRcys equations. Among eGFRcr equations, CKD-EPI 2009 and CKD-EPI 2021 showed larger bias and lower P30 than EKFC 2021 and RLM. There were no meaningful differences in performance across eGFRcys equations. Findings were consistent across comorbid conditions, and eGFRcr-cys equations showed good performance in patients with liver disease, cancer and heart failure.

CONCLUSIONS

In conclusion, eGFRcr-cys equations performed best, with minimal variation among equations in this Swedish cohort. The lower performance of CKD-EPI eGFRcr equations compared with EKFC and RLM may reflect differences in population characteristics and mGFR methods. Implementing eGFRcr equations will require a trade-off between accuracy and uniformity across regions.

Comparison and evaluation of the 2009 and 2021 chronic kidney disease-epidemiological collaboration equations among Jordanian patients with type 2 diabetes mellitus

AIMS

This study compared the 2009 versus 2021 chronic kidney disease (CKD) Epidemiological Collaboration (CKD-EPI) equations to calculate estimated glomerular filtration rate (eGFR) among Jordanian patients with T2DM to assess their agreement and impact on CKD staging.

METHODS

This cross-sectional study included 2382 adult Jordanian patients with T2DM. The 2009 and 2021 CKD-EPI equations were used to calculate eGFR. Patients were reclassified according to kidney disease-Improving Global Outcomes (KDIGO) categories. Agreement between the equations was assessed using Bland-Altman plots and Lin's concordance correlation.

RESULTS

The 2021 equation significantly increased eGFR by a median of 2.1 mL/min/1.73 m2 (interquartile range: 0.6-3.6 mL/min/1.73 m2). However, there was significant agreement between equations (Kappa: 0.99; 95% confidence interval: 0.95-1.00), independent of age, sex, and the presence of hypertension. In total, 202 patients (8.5%) were reclassified to higher KDIGO categories using the 2021 equation, with category G3 being most affected. The overall prevalence of patients in the high to highest risk categories decreased (28.0% vs. 26.5%).

CONCLUSIONS

Although there was significant agreement with the 2009 equation, the 2021 equation increased eGFR and resulted in the reclassification of a subset of subjects according to KDIGO criteria. The uncertain impact of reducing high-risk category patients raises concerns about potential delays in referral and intervention, while holding the potential to enhance high-risk patient categorization, thus alleviating healthcare burden.

Glomerular Filtration Rate Estimation in Adults: Myths and Promises

BACKGROUND

In daily practice, glomerular filtration rate (GFR) is estimated with equations including renal biomarkers. Among these biomarkers, serum creatinine remains the most used. However, there are many limitations with serum creatinine, which we will discuss in the current review. We will also discuss how creatinine-based equations have been developed and what we can expect from them in terms of performance to estimate GFR.

SUMMARY

Different creatinine-based equations have been proposed. We will show the advantages of the recent European Kidney Function Consortium equation. This equation can be used in children and adults. This equation can also be used with some flexibility in different populations.

KEY MESSAGES

GFR is estimated by creatinine-based equations, but the most important for nephrologists is probably to know the limitations of these equations.

CKD-EPI and EKFC GFR Estimating Equations: Performance and Other Considerations for Selecting Equations for Implementation in Adults

SIGNIFICANCE STATEMENT

New eGFR equations from Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and European Kidney Function Consortium (EKFC) using creatinine (eGFRcr), cystatin C (eGFRcys), and both (eGFRcr-cys) have sufficient accuracy for use in clinical practice, leading to uncertainty in selecting equations for implementation. The authors evaluated performance of equations in an independent population of 4050 adults and evaluated other considerations important for implementation. They found that CKD-EPI and EKFC equations are approaching convergence, with better performance of eGFRcr-cys equations in the overall group and fewer differences among race, sex, and age subgroups than eGFRcr equations. Larger differences among eGFRcr equations reflect regional population differences in creatinine, forcing a trade-off between accuracy and uniformity in global implementation of eGFRcr equations. More widespread use of cystatin C could avoid this trade-off.

BACKGROUND

New CKD-EPI and EKFC eGFR equations using eGFRcr, eGFRcys, and both (eGFRcr-cys) have sufficient accuracy for use in clinical practice. A better understanding of the equations, including their performance in race, sex and age subgroups, is important for selection of eGFR equations for global implementation.

METHODS

We evaluated performance (bias and P 30 ) of equations and methods used for equation development in an independent study population comprising 4050 adults pooled from 12 studies. The mean (SD) measured GFR was 76.4 (29.6) ml/min per 1.73 m 2 and age 57.0 (17.4) years, with 1557 (38%) women and 579 (14%) Black participants.

RESULTS

Coefficients for creatinine, cystatin C, age, and sex in the CKD-EPI and EKFC equations are similar. Performance of the eGFRcr-cys equations in the overall population (bias <±5 ml/min per 1.73 m 2 and P 30 >90%) was better than the eGFRcr or eGFRcys equations, with fewer differences among race, sex, and age subgroups. Differences in performance across subgroups reflected differences in diversity of source populations and use of variables for race and sex for equation development. Larger differences among eGFRcr equations reflected regional population differences in non-GFR determinants of creatinine.

CONCLUSION

CKD-EPI and EKFC equations are approaching convergence. It is not possible to maximize both accuracy and uniformity in selecting one of the currently available eGFRcr equations for implementation across regions. Decisions should consider methods for equation development in addition to performance. Wider use of cystatin C with creatinine could maximize both accuracy and uniformity of GFR estimation using currently available equations.

Estimating glomerular filtration rate with new equations: can one size ever fit all?

Glomerular filtration rate (GFR) is thought to be the best overall indicator of kidney health. On an individual patient basis, a working knowledge of GFR is important to understand the future risk for chronic kidney disease (CKD) progression, enhanced risk for cardiovascular disease and death, and for optimal medical management including the dosing of certain drugs. Although GFR can be directly measured using exogenous compounds that are eliminated by the kidney, these methods are not scalable for repeated and routine use in clinical care. Thus, in most circumstances GFR is estimated, termed estimated GFR (eGFR), using serum biomarkers that are eliminated by the kidney. Of these, serum creatinine, and to a lesser extent cystatin C, are most widely employed. However, the resulting number is simply a population average for an individual of that age and sex with a given serum creatinine and/or cystatin C, while the range of potential GFR values is actually quite large. Thus, it is important to consider characteristics of a given patient that might make this estimate better or worse in a particular case. In some circumstances, cystatin C or creatinine might be the better choice. Ultimately it is difficult, if not impossible, to have an eGFR equation that performs equally well in all populations. Thus, in certain cases it might be appropriate to directly measure GFR for high consequence medical decision-making, such as approval for kidney donation or prior to certain chemotherapeutic regimens. In all cases, the eGFR thresholds of CKD stage should not be viewed as absolute numbers. Thus, clinical care should not be determined solely by CKD stage as determined by eGFR alone, but rather by the combination of an individual patient's likely kidney function together with their current clinical situation.

Effect of serum creatinine difference between the Jaffe and the enzymatic method on kidney disease detection and staging

Background

Serum creatinine (SCr), mainly determined by the Jaffe or an enzymatic method, is the central marker to assess kidney function. Deviations between these two methods may affect the diagnosis and staging of acute kidney injury (AKI) and chronic kidney disease (CKD).

Methods

The results of the first parallel SCr measurement (Jaffe and enzymatic method) of adult in- and outpatients in the same serum sample at the University Hospital Essen (Essen, Germany) between 2020-2022 were retrospectively evaluated. A Bland-Altman plot with 95% limits of agreement (LoAs) was used to assess the difference between the Jaffe and the enzymatic SCr (eSCr) method. We used the 2009 Chronic Kidney Disease Epidemiology Collaboration equation for determination of estimated glomerular filtration rate (eGFR) according to the Kidney Disease: Improving Global Outcomes guidelines.

Results

A total of 41 144 parallel SCr measurements were evaluated. On average, Jaffe SCr was 0.07 mg/dl higher than eSCr (LoA -0.12; 0.25 mg/dl). In 19% of all cases there was a different CKD stage when comparing eGFR between both SCr methods, of which 98% resulted in a more severe CKD stage determined with Jaffe SCr. In 1.6% of all cases Jaffe SCr was ≥0.3 mg/dl higher than eSCr.

Conclusion

The present study showed that methods of SCr measurement may affect both the diagnosis and staging of AKI and CKD. This must be taken into account when interpreting measurements of renal function in everyday clinical practice, but also when planning and comparing studies on renal diseases. One should therefore stay with one method for SCr measurement, preferably with the enzymatic method.

New and old GFR equations: a European perspective

Glomerular filtration rate (GFR) is estimated in clinical practice from equations based on the serum concentration of endogenous biomarkers and demographic data. The 2009 creatinine-based Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI2009) was recommended worldwide until 2021, when it was recalibrated to remove the African-American race factor. The CKD-EPI2009 and CKD-EPIcr2021 equations overestimate GFR of adults aged 18-30 years, with a strong overestimation in estimated GFR (eGFR) at age 18 years. CKD-EPICr2021 does not perform better than CKD-EPI2009 in US population, overestimating GFR in non-Black subjects, and underestimating it in Black subjects with the same magnitude. CKD-EPICr2021 performed worse than the CKD-EPI2009 in White Europeans, and provides no or limited performance gains in Black European and Black African populations. The European Kidney Function Consortium (EKFC) equation, which incorporates median normal value of serum creatinine in healthy population, overcomes the limitations of the CKD-EPI equations: it provides a continuity of eGFR at the transition between pediatric and adult care, and performs reasonably well in diverse populations, assuming dedicated scaling of serum creatinine (Q) values is used. The new EKFC equation based on cystatin C (EKFCCC) shares the same mathematical construction, namely, it incorporates the median cystatin C value in the general population, which is independent of sex and ethnicity. EKFCCC is therefore a sex-free and race-free equation, which performs better than the CKD-EPI equation based on cystatin C. Despite advances in the field of GFR estimation, no equation is perfectly accurate, and GFR measurement by exogenous tracer clearance is still required in specific populations and/or specific clinical situations.

Development and validation of a new equation based on plasma creatinine and muscle mass assessed by CT scan to estimate glomerular filtration rate: a cross-sectional study

Background

Inter-individual variations of non-glomerular filtration rate (GFR) determinants of serum creatinine, such as muscle mass, account for the imperfect performance of estimated GFR (eGFR) equations. We aimed to develop an equation based on creatinine and total lumbar muscle cross-sectional area measured by unenhanced computed tomography scan at the third lumbar vertebra.

Methods

The muscle mass-based eGFR (MMB-eGFR) equation was developed in 118 kidney donor candidates (iohexol clearance) using linear regression. Validation cohorts included 114 healthy subjects from another center (⁵¹Cr-EDTA clearance, validation population 1), 55 patients with chronic diseases (iohexol, validation population 2), and 60 patients with highly discordant creatinine and cystatin C-based eGFR, thus presumed to have atypical non-GFR determinants of creatinine (⁵¹Cr-EDTA, validation population 3). Mean bias was the mean difference between eGFR and measured GFR, precision the standard deviation (SD) of the bias, and accuracy the percentage of eGFR values falling within 20% and 30% of measured GFR.

Results

In validation population 1, performance of MMB-eGFR was not different from those of CKD-EPI_Cr2009 and CKD-EPI_Cr2021. In validation population 2, MMB-eGFR was unbiased and displayed better precision than CKD-EPI_Cr2009, CKD-EPI_Cr2021 and EKFC (SD of the biases: 13.1 vs 16.5, 16.8 and 15.9 mL/min/1.73 m²). In validation population 3, MMB-eGFR had better precision and accuracy {accuracy within 30%: 75.0% [95% confidence interval (CI) 64.0-86.0] vs 51.5% (95% CI 39.0-64.3) for CKD-EPI_Cr2009, 43.3% (95% CI 31.0-55.9) for CKD-EPICr2021, and 53.3% (95% CI 40.7-66.0) for EKFC}. Difference in bias between Black and white subjects was -2.1 mL/min/1.73 m² (95% CI -7.2 to 3.0), vs -8.4 mL/min/1.73 m² (95% CI -13.2 to -3.6) for CKD-EPI_Cr2021.

Conclusion

MMB-eGFR displayed better performances than equations based on demographics, and could be applied to subjects of various ethnic backgrounds.

Rationale and Design of the Diet, CKD, and Apolipoprotein L1 Study in Low-Income and Middle-Income Countries

Introduction

Diet, chronic kidney disease (CKD), and Apolipoprotein L1 (APOL1) (DCA) Study is examining the role of dietary factors in CKD progression and APOL1 nephropathy. We describe enrollment and retention efforts and highlight facilitators and barriers to enrollment and operational challenges, as well as accommodations made in the study protocol.

Methods

The DCA study is enrolling participants in 7 centers in West Africa. Participants who consented were invited to complete dietary recalls and 24-hour urine collections in year 1. We conducted focus groups and semistructured interviews among study personnel to identify facilitators and barriers to enrollment as well as retention and operational challenges in the execution of the study protocol. We analyzed emerging themes using content analyses.

Results

A total of 712 participants were enrolled in 18 months with 1256 24-hour urine and 1260 dietary recalls. Barriers to enrollment were the following: (i) a lack of understanding of research, (ii) the burden of research visits, and (iii) incorporating cultural and traditional nuances when designing research protocols. Factors facilitating enrollment were the following: (i) designing convenient research visits, (ii) building rapport and increased communication between the research team and participants, and (iii) cultural sensitivity - adapting research protocols for the populations involved. Offering home visits, providing free dietary counseling, reducing the volume of study blood collection, and reducing the frequency of visits were some changes made in the study protocol that increased participant satisfaction.

Conclusion

Adopting a participant-centered approach with accommodations in the protocol for cultural adaptability and incorporating participant feedback is vital for carrying out research in low-income and middle-income regions.

Natural course and determinants of short-term kidney function decline in hereditary transthyretin amyloidosis: a French observational study

Data regarding renal involvement in patients with hereditary transthyretin (ATTRv) amyloidosis are scarce and the natural course of chronic kidney disease (CKD) in this population remains unclear. This observational study, including adult patients diagnosed with ATTRv amyloidosis at the French Reference Centre for Cardiac Amyloidosis, investigated renal function outcome and its determinants. Multivariable logistic regression models identified factors associated with CKD at baseline. Determinants of the change in estimated glomerular filtration rate (eGFR) over 24 months of follow-up were assessed with a multivariable linear mixed-effects model. In total, 232 patients (78 women [34%], mean age: 64 years) with ATTRv amyloidosis were classified on the basis of their TTR variants: ATTRV122I (37%), ATTRV30M (29%), and other variants (34%). Median baseline eGFR was 78 ml/min/1.73 m². Seventy-two patients (31%) had an eGFR below 60 ml/min/1.73m² and 27/137 patients (20%) had significant proteinuria (urine protein/creatinine ratio ≥30 mg/mmol). Renal biopsy, performed in four cases, found typical Congo red-positive and TTR-labelled amyloid deposits in all cases. Older age (OR 1.07, p < .001) and a prior history of hypertension (OR 2.09, p = .04) were associated with a higher prevalence of CKD at baseline, whereas higher left ventricular global longitudinal strain (LVGLS) (OR 0.83, p < .001) was associated with a lower prevalence. The estimated change in eGFR was -7.12 [-9.61, -4.63] and -8.21 [-10.81, -5.60] ml/min/1.73 m² after 12 and 24 months of follow-up, respectively. eGFR decline was independently associated with older age ((67-74], coefficient= -14.35 mL/min/1.73 m², p < .01, >74, coefficient = -22.93 mL/min/1.73 m², p < .001, versus <56), ATTRV122I (coefficient = -17.17 mL/min/1.73m², p < .01, versus ATTRV30M) and LVGLS (coefficient = 1.22, p < .01). These data suggest that CKD is a common finding in patients with ATTRv amyloidosis, and that eGFR decline is rapid during the first year of evaluation. Older age, lower LVGLS and ATTRV122I were associated with a worse renal outcome. Further studies are now needed to evaluate effects of new targeted therapies on long term renal function.

2009 CKD-EPI glomerular filtration rate estimation in Black individuals outside the United States: a systematic review and meta-analysis

Background

The 2009 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is the most used equation to estimate glomerular filtration rate (GFR), with race being a factor thereof, increasing GFR by 16% in self-identified Black persons compared with non-Black persons. However, recent publications indicate that it might overestimate GFR for Black adults outside the USA. In this meta-analysis, we assessed the accuracy, evaluated by the percentage of estimated GFR within 30% of measured GFR (P30), of the 2009 CKD-EPI equation in estimating GFR with and without the race coefficient in Black individuals outside the United States of America (USA).

Methods

We searched MEDLINE and Embase from inception to 9 July 2022, with no language restriction, supplemented by manual reference searches. Studies that assessed the CKD-EPI P30 accuracy with or without the race coefficient in Black adults outside the USA with an adequate method of GFR measurement were included. Data were extracted by independent pairs of reviewers and were pooled using a random-effects model.

Results

We included 11 studies, with a total of 1834 Black adults from South America, Africa and Europe. The race coefficient in the 2009 CKD-EPI equation significantly decreased P30 accuracy {61.9% [95% confidence interval (CI) 53-70%] versus 72.9% [95% CI 66.7-78.3%]; P = .03}.

Conclusions

Outside the USA, the 2009 CKD-EPI equation should not be used with the race coefficient, even though the 2009 CKD-EPI equation is not sufficiently accurate either way (<75%). Thus we endorse the Kidney Disease: Improving Global Outcomes guidelines to use exogenous filtration markers when this may impact clinical conduct.

The new, race-free, Chronic Kidney Disease Epidemiology Consortium (CKD-EPI) equation to estimate glomerular filtration rate: is it applicable in Europe? A position statement by the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

The EFLM recommends not to implement the race-free Chronic Kidney Disease Epidemiology Consortium (CKD-EPI) equation in European laboratories and to keep the 2009 version of the CKD-EPI equation, without applying a race correction factor. This recommendation is completely in line with a recent Editorial published by the European Renal Association who has also proposed to change to a novel equation only when it has considerably better performance, trying to reach global consensus before implementing such a new glomerular filtration rate (GFR) estimation equation. In Europe, this equation could be for instance the new European Kidney Function Consortium (EKFC) equation, which is population-specific, developed from European cohorts and accurate from infants to the older old. Beyond serum creatinine, the estimating equations based on cystatin C will probably gain in popularity, especially because cystatin C seems independent of race. Finally, we must keep in mind that all GFR equations remain an estimation of GFR, especially rough at the individual level. Measuring GFR with a reference method, such as iohexol clearance, remains indicated in specific patients and/or specific situations, and here also, the role of the clinical laboratories is central and should still evolve positively in the future.

Cystatin C-Based Equation to Estimate GFR without the Inclusion of Race and Sex

BACKGROUND

The accuracy of estimation of kidney function with the use of routine metabolic tests, such as measurement of the serum creatinine level, has been controversial. The European Kidney Function Consortium (EKFC) developed a creatinine-based equation (EKFC eGFRcr) to estimate the glomerular filtration rate (GFR) with a rescaled serum creatinine level (i.e., the serum creatinine level is divided by the median serum creatinine level among healthy persons to control for variation related to differences in age, sex, or race). Whether a cystatin C-based EKFC equation would increase the accuracy of estimated GFR is unknown.

METHODS

We used data from patients in Sweden to estimate the rescaling factor for the cystatin C level in adults. We then replaced rescaled serum creatinine in the EKFC eGFRcr equation with rescaled cystatin C, and we validated the resulting EKFC eGFRcys equation in cohorts of White patients and Black patients in Europe, the United States, and Africa, according to measured GFR, levels of serum creatinine and cystatin C, age, and sex.

RESULTS

On the basis of data from 227,643 patients in Sweden, the rescaling factor for cystatin C was estimated at 0.83 for men and women younger than 50 years of age and 0.83 + 0.005 × (age - 50) for those 50 years of age or older. The EKFC eGFRcys equation was unbiased, had accuracy that was similar to that of the EKFC eGFRcr equation in both White patients and Black patients (11,231 patients from Europe, 1093 from the United States, and 508 from Africa), and was more accurate than the Chronic Kidney Disease Epidemiology Collaboration eGFRcys equation recommended by Kidney Disease: Improving Global Outcomes. The arithmetic mean of EKFC eGFRcr and EKFC eGFRcys further improved the accuracy of estimated GFR over estimates from either biomarker equation alone.

CONCLUSIONS

The EKFC eGFRcys equation had the same mathematical form as the EKFC eGFRcr equation, but it had a scaling factor for cystatin C that did not differ according to race or sex. In cohorts from Europe, the United States, and Africa, this equation improved the accuracy of GFR assessment over that of commonly used equations. (Funded by the Swedish Research Council.).

Performance of creatinine-based equations to estimate glomerular filtration rate in White and Black populations in Europe, Brazil and Africa

BACKGROUND

A new Chronic Kidney Disease Epidemiology Collaboration equation without the race variable has been recently proposed (CKD-EPIAS). This equation has neither been validated outside USA nor compared with the new European Kidney Function Consortium (EKFC) and Lund-Malmö Revised (LMREV) equations, developed in European cohorts.

METHODS

Standardized creatinine and measured glomerular filtration rate (GFR) from the European EKFC cohorts (n = 13 856 including 6031 individuals in the external validation cohort), from France (n = 4429, including 964 Black Europeans), from Brazil (n = 100) and from Africa (n = 508) were used to test the performances of the equations. A matched analysis between White Europeans and Black Africans or Black Europeans was performed.

RESULTS

In White Europeans (n = 9496), both the EKFC and LMREV equations outperformed CKD-EPIAS (bias of -0.6 and -3.2, respectively versus 5.0 mL/min/1.73 m², and accuracy within 30% of 86.9 and 87.4, respectively, versus 80.9%). In Black Europeans and Black Africans, the best performance was observed with the EKFC equation using a specific Q-value (= concentration of serum creatinine in healthy males and females). These results were confirmed in matched analyses, which showed that serum creatinine concentrations were different in White Europeans, Black Europeans and Black Africans for the same measured GFR, age, sex and body mass index. Creatinine differences were more relevant in males.

CONCLUSION

In a European and African cohort, the performances of CKD-EPIAS remain suboptimal. The EKFC equation, using usual or dedicated population-specific Q-values, presents the best performance in the whole age range in the European and African populations included in this study.

MicroRNAs Associated with Chronic Kidney Disease in the General Population and High-Risk Subgroups-A Systematic Review

The potential utility of microRNAs (miRNAs) as diagnostic or prognostic biomarkers, as well as therapeutic targets, for chronic kidney disease (CKD) has been advocated. However, studies evaluating the expression profile of the same miRNA signatures in CKD report contradictory findings. This review aimed to characterize miRNAs associated with CKD and/or measures of kidney function and kidney damage in the general population, and also in high-risk subgroups, including people with hypertension (HTN), diabetes mellitus (DM) and human immunodeficiency virus (HIV) infection. Medline via PubMed, Scopus, Web of Science, and EBSCOhost databases were searched to identify relevant studies published in English or French languages on or before 30 September 2022. A total of 75 studies fulfilled the eligibility criteria: CKD (n = 18), diabetic kidney disease (DKD) (n = 51) and HTN-associated CKD (n = 6), with no study reporting on miRNA profiles in people with HIV-associated nephropathy. In individuals with CKD, miR-126 and miR-223 were consistently downregulated, whilst in DKD, miR-21 and miR-29b were consistently upregulated and miR-30e and let-7a were consistently downregulated in at least three studies. These findings suggest that these miRNAs may be involved in the pathogenesis of CKD and therefore invites further research to explore their clinical utility for CKD prevention and control.

The New 2021 CKD-EPI Equation Without Race in a European Cohort of Renal Transplanted Patients

BACKGROUND

Whether the new chronic kidney disease-epidemiology (CKD-EPI) equation without the race variable remains accurate enough for glomerular filtration rate (GFR) estimation in non-US kidney transplant recipients (KTRs) is unclear. We sought to compare the predictive performance between this equation and the classical CKD-EPI equation in a French cohort of KTRs. We also evaluated the performance of the European Kidney Function Consortium (EKFC) equation, an estimate that has proved very accurate in nontransplant patients and that does not include race variable.

METHODS

We retrospectively selected 489 KTRs for whom GFR was measured by inulin clearance. Performances of GFR equations were compared according to median bias, imprecision, and accuracy within 30% (P30) and 20% (P20). Differences in P20/P30 were tested using the exact McNemar test.

RESULTS

Although the 4 equations exhibited a similar level of imprecision, the bias of the new CKD-EPI equation was +5.5 (4.0; 6.6) mL/min/1.73 m², much higher than the bias of the classical CKD-EPI, EKFC, and Modified Diet in Renal Diseases (MDRD) equation (2.4 [1.7;3.5], 2.2 [1.1;3.1], and -0.5 [-1.5; 1.0] mL/min/1.73 m², respectively). The new CKD-EPI equation was significantly less accurate with a P30 of 68.3% as compared with 74.2%, 75.3%, and 77.1% for the classical CKD-EPI, EKFC, and MDRD equation, respectively. The EKFC equation outperformed both versions of the CKD-EPI equation in terms of P20.

CONCLUSIONS

The new CKD-EPI equation is suboptimal for the care and follow-up of European transplanted patients. The EKFC equation shows at least a similar performance to the MDRD and the classical CKD-EPI equation. Further validation of the EKFC equation in KTRs from a diverse ethnic background is needed.

Time to Rethink the Current Paradigm for Assessing Kidney Function in Drug Development and Beyond

Chronic kidney disease (CKD) is an important health issue that affects ~ 9.1% of the world adult population. Serum creatinine is the most commonly used biomarker for assessing kidney function and is utilized in different equations for estimating creatinine clearance or glomerular filtration rate (GFR). The Cockcroft-Gault formula for adults and "original" Schwartz formula for children have been the most commonly used equations for estimating kidney function during the last 3-4 decades. Introduction of standardized serum creatinine bioanalytical methodology has reduced interlaboratory variability but is not intended to be used with Cockcroft-Gault or original Schwartz equations. More accurate equations (for instance, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) for adults and bedside Schwartz or Chronic Kidney Disease in Children Schwartz equation for children) based on standardized serum creatinine values (and another biomarker-cystatin C) have been introduced and validated in recent years. Recently, the CKD-EPI equation refitted without a race variable was introduced. Clinical practice guidance in nephrology advocates a shift to these equations for managing health care of patients with CKD. The guidance also recommends use of albuminuria in addition to GFR for CKD diagnosis and management. Significant research with large data sets would be necessary to evaluate whether this paradigm would also be valuable in drug dose adjustments. This article attempts to highlight some important advancements in the field from a clinical pharmacology perspective and is a call to action to industry, regulators, and academia to rethink the current paradigm for assessing kidney function to enable dose recommendation in patients with CKD.

Systematic review of international studies evaluating MDRD and CKD-EPI estimated glomerular filtration rate (eGFR) equations in Black adults

Use of race adjustment in estimating glomerular filtration rate (eGFR) has been challenged given concerns that it may negatively impact the clinical care of Black patients, as it results in Black patients being systematically assigned higher eGFR values than non-Black patients. We conducted a systematic review to assess how well eGFR, with and without race adjustment, estimates measured GFR (mGFR) in Black adults globally. A search across multiple databases for articles published from 1999 to May 2021 that compared eGFR to mGFR and reported outcomes by Black race was performed. We included studies that assessed eGFR using the Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPICr) creatinine equations. Risk of study bias and applicability were assessed with the QUality Assessment of Diagnostic Accuracy Studies-2. Of 13,167 citations identified, 12 met the data synthesis criteria (unique patient cohorts in which eGFR was compared to mGFR with and without race adjustment). The studies included patients with and without kidney disease from Africa (n = 6), the United States (n = 3), Europe (n = 2), and Brazil (n = 1). Of 11 CKD-EPI equation studies, all assessed bias, 8 assessed accuracy, 6 assessed precision, and 5 assessed correlation/concordance. Of 7 MDRD equation studies, all assessed bias, 6 assessed accuracy, 5 assessed precision, and 3 assessed correlation/concordance. The majority of studies found that removal of race adjustment improved bias, accuracy, and precision of eGFR equations for Black adults. Risk of study bias was often unclear, but applicability concerns were low. Our systematic review supports the need for future studies to be conducted in diverse populations to assess the possibility of alternative approaches for estimating GFR. This study additionally provides systematic-level evidence for the American Society of Nephrology-National Kidney Foundation Task Force efforts to pursue other options for GFR estimation.

Associations between different eGFR estimating equations and mortality for CVD patients: A retrospective cohort study based on the NHANES database

To assess the associations of eGFRCKD-EPI (estimated glomerular filtration rate (eGFR) by chronic kidney disease epidemiology collaboration equation), eGFRMDRD (eGFR by modification of diet in renal disease), and serum creatinine (scr) on the death for American people diagnosed with cardiovascular disease (CVD) respectively, and to compare the predicted performance of eGFRCKD-EPI, eGFRMDRD, and scr. A total of 63,078 participants who derived from the National Health and Nutrition Examination Survey (NHANES) database, were obtained in this retrospective cohort study, and collected the baseline characteristics all participants. The outcomes of our study were defined as death, and eGFR estimating equations was defined as eGFRCKD-EPI, eGFRMDRD, and scr. Univariate and multivariate COX analysis were performed to assess the relationship. A subgroup analysis was conducted based on whether patients had anemia. Simultaneously, we also considered the predictive value of eGFRCKD-EPI, eGFRMDRD, and scr in the risk of death. All patients were followed for at most 5-years. After excluded participants who did not meet the inclusion criteria and had missing information, the present study included 2419 participants ultimately, and were divided into alive group (n = 1800) and dead group (n = 619). The mortality rate for CVD patients in this study was approximately 25.59% at the end of follow-up. After adjustment for covariates, the result showed that participants with eGFRCKD-EPI/eGFRMDRD < 30 mL/min/1.73 m2 or 30 to 45 mL/min/1.73 m2 had a higher risk of mortality. Similarly, participants with scr (Q4 ≥ 1.2) were associated with the increased risk of death. Additionally, eGFRCKD-EPI has a higher predictive value in 1-year, 3-years, and 5-years risk of death among patients with CVD than eGFRMDRD and scr. The lower level of eGFR was associated with higher risk of death among American population diagnosed with CVD, especially for non-anemic patients. Importantly, our study also displayed that CKD-EPI-based calculation equation of eGFR (eGFRCKD-EPI) provided for a better predictive value than eGFRMDRD and scr in the risk of death.

The need for screening, early diagnosis, and prediction of chronic kidney disease in people with diabetes in low- and middle-income countries-a review of the current literature

Chronic kidney disease (CKD) in people with diabetes is becoming an increasing major public health concern, disproportionately burdening low- and middle-income countries (LMICs). This rising burden is due to various factors, including the lack of disease awareness that results in late referral and the cost of screening and consequent treatment of the comorbid conditions, as well as other factors endemic to LMICs relating to inadequate management of risk factors. We critically assessed the extant literature, by performing searches of Medline via PubMed, EBSCOhost, Scopus, and Web of Science, for studies pertaining to screening, diagnosis, and prediction of CKD amongst adults with diabetes in LMICs, using relevant key terms. The relevant studies were summarized through key themes derived from the Wilson and Jungner criteria. We found that screening for CKD in people with diabetes is generally infrequent in LMICs. Also, LMICs are ill-equipped to appropriately manage diabetes-associated CKD, especially its late stages, in which supportive care and kidney replacement therapy (KRT) might be required. There are acceptable and relatively simple tools that can aid diabetes-associated CKD screening in these countries; however, these tools come with limitations. Thus, effective implementation of diabetes-associated CKD screening in LMICs remains a challenge, and the cost-effectiveness of such an undertaking largely remains to be explored. In conclusion, for many compelling reasons, screening for CKD in people with diabetes should be a high policy priority in LMICs, as the huge cost associated with higher mortality and morbidity in this group and the cost of KRT offers a compelling economic incentive for improving early detection of diabetes in CKD.

Measurement of kidney function in Malawi, South Africa, and Uganda: a multicentre cohort study

BACKGROUND

The burden of kidney disease in many African countries is unknown. Equations used to estimate kidney function from serum creatinine have limited regional validation. We sought to determine the most accurate way to measure kidney function and thus estimate the prevalence of impaired kidney function in African populations.

METHODS

We measured serum creatinine, cystatin C, and glomerular filtration rate (GFR) using the slope-intercept method for iohexol plasma clearance (mGFR) in population cohorts from Malawi, Uganda, and South Africa. We compared performance of creatinine and cystatin C-based estimating equations to mGFR, modelled and validated a new creatinine-based equation, and developed a multiple imputation model trained on the mGFR sample using age, sex, and creatinine as the variables to predict the population prevalence of impaired kidney function in west, east, and southern Africa.

FINDINGS

Of 3025 people who underwent measured GFR testing (Malawi n=1020, South Africa n=986, and Uganda n=1019), we analysed data for 2578 participants who had complete data and adequate quality measurements. Among 2578 included participants, creatinine-based equations overestimated kidney function compared with mGFR, worsened by use of ethnicity coefficients. The greatest bias occurred at low kidney function, such that the proportion with GFR of less than 60 mL/min per 1·73 m² either directly measured or estimated by cystatin C was more than double that estimated from creatinine. A new creatinine-based equation did not outperform existing equations, and no equation, including the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2021 race-neutral equation, estimated GFR within plus or minus 30% of mGFR for 75% or more of the participants. Using a model to impute kidney function based on mGFR, the estimated prevalence of impaired kidney function was more than two-times higher than creatinine-based estimates in populations across six countries in Africa.

INTERPRETATION

Estimating GFR using serum creatinine substantially underestimates the individual and population-level burden of impaired kidney function in Africa with implications for understanding disease progression and complications, clinical care, and service provision. Scalable and affordable ways to accurately identify impaired kidney function in Africa are urgently needed.

FUNDING

The GSK Africa Non-Communicable Disease Open Lab.

TRANSLATIONS

For the Luganda, Chichewa and Xitsonga translations of the abstract see Supplementary Materials section.

Comparison of the prevalence of kidney disease by proteinuria and decreased estimated glomerular filtration rate determined using three creatinine-based equations among patients admitted on medical wards of Masaka Regional Referral Hospital in Uganda: a prospective study

Background

Despite estimated glomerular filtration rate (eGFR) being the best marker for kidney function, there are no studies in sub-Saharan Africa comparing the performance of various equations used to determine eGFR. We compared prevalence of kidney disease determined by proteinuria of ≥  + 1 and or kidney disease improving global outcomes (KDIGO) eGFR criteria of < 60 ml/minute/1.73m² determined using three creatinine-based equations among patients admitted on medical ward of Masaka Regional Referral Hospital.

Methods

This was a prospective study conducted among adult patients admitted on medical wards between September 2020 to March 2021. Spot urine samples were collected to assess for proteinuria and blood samples were collected to assess serum creatinine levels. Kidney disease was defined as proteinuria of ≥ 1 + on spot urine dipstick and or KDIGO eGFR criteria of < 60 ml/minute/1.73m². Estimated glomerular filtration rate was calculated using three creatinine-based equations: a) Full Age Spectrum equation (FAS), b) chronic kidney disease-Epidemiology collaboration (CKD-EPI) 2021 equation, c) CKD EPI 2009 (without and with race factor) equation. CKD was determined after followed up at 90 days post enrollment to determine the chronicity of proteinuria of ≥  + 1 and or KDIGO eGFR criteria of < 60mls /minute/1.73m². We also compared prevalence of CKD determined by KDIGO eGFR criteria of < 60mls /minute/1.73m² vs age adapted eGFR threshold criteria for defining CKD.

Results

Among the 357 patients enrolled in the study, KDIGO eGFR criteria of < 60mls / minute determined using FAS and CKD-EPI 2009 without race factor equations and or proteinuria of ≥  + 1 showed the highest overall prevalence of kidney disease at 27.2%.

Prevalence of confirmed CKD at 90 days was highest with proteinuria ≥  + 1 and or KDIGO eGFR criteria of < 60mls/min determined using CKD EPI 2009 without race factor Equation (15.1%).

Conclusions

Use of KDIGO eGFR criteria of < 60mls / minute /1.73m² using FAS and CKD-EPI 2009 without race equations identifies the largest number of patients with CKD. Health care systems in sub-Saharan Africa should calculate eGFR using FAS equations or CKD-EPI 2009 without race equations during basic screening and management protocols.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02865-w.

Kidney Function Assessment in African American Patients: A Narrative Review for Pharmacists

Recent recognitions of longstanding societal inequity in kidney function assessments have prompted the call to eliminate race as part of the algorithm to assess estimated glomerular filtration rate (eGFR). Previous equations for eGFR estimation adopted race as part of the calculation. Incorporating race within eGFR equations results in overestimating and underestimating Black and nonblack patients, respectively. The inclusion of race is controversial. In September 2021, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) combined task force recommended estimating the kidney function without using a race variable. The task force endorsed race-free creatinine-cystatin C equations to be more accurate than the creatinine-only equations. Before the application of NKF-ASN revised recommendations, major healthcare disparities influenced daily clinical practice. Those disparities include the delay in initiating medications that have reanl or cardio-protective effects, such as sodium-glucose cotransporter–2 inhibitors (SGLT-2i) and angiotensin-converting enzyme inhibitors (ACEIs). Clinical judgment should be employed when dose adjusting medications. Combining the eGFR with other clinical assessment tools such as urinary output, the expanded use of confirmatory tests, and the eGFR trend is suggested for a better kidney function assessment. Additionally, creatinine-cystatin C is recommended when feasible, and when institutions have the laboratory abilities.

Large difference but high correlation between creatinine and cystatin C estimated glomerular filtration rate in Mesoamerican sugarcane cutters

OBJECTIVES

To explore the relationship between creatinine and cystatin C based estimated glomerular filtration rate (eGFR) in actively working sugarcane cutters.

METHODS

This cohort study included 458 sugarcane cutters from Nicaragua and El Salvador. Serum samples were taken before and at end of harvest seasons and analysed for creatinine and cystatin C. Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formulas were used to calculate eGFRs based on creatinine (eGFR_cr), cystatin C (eGFR_cys) and both creatinine and cystatin C (eGFR_crcys) at each time point. Bland-Altman plots and paired t-tests were used to compare the difference between eGFR_cr and eGFR_cys, and the difference in eGFRs between before and at end of the harvest seasons.

RESULTS

The mean eGFR_cr was higher than eGFR_cys in both cohorts; absolute difference 22 mL/min/1.73 m² (95% CI 21 to 23) in Nicaragua and 13 mL/min/1.73 m² (95% CI 11 to 15) in El Salvador. Correlations between eGFR_cr and eGFR_cys were high, with r=0.69, 0.77 and 0.67 in Nicaragua at pre-harvest, end-harvest and cross-harvest, and r=0.89, 0.89 and 0.49 in El Salvador.

CONCLUSIONS

Creatinine increases among heat-stressed workers reflect reduced glomerular filtration as estimated using eGFR_cys, a marker independent of muscle mass and metabolism. The discrepancy between eGFR_cr and eGFR_cys may indicate reduced glomerular filtration of larger molecules and/or systemic bias in CKD-EPI performance in this population.

Estimating Renal Function Following Lung Transplantation

Background: Patients undergoing lung transplantation (LTx) experience a rapid decline in glomerular filtration rate (GFR) in the acute postoperative period. However, no prospective longitudinal studies directly comparing the performance of equations for estimating GFR in this patient population currently exist. Methods: In total, 32 patients undergoing LTx met the study criteria. At pre-LTx and 1-, 3-, and 12-weeks post-LTx, GFR was determined by ⁵¹Cr-EDTA and by equations for estimating GFR based on plasma (P)-Creatinine, P-Cystatin C, or a combination of both. Results: Measured GFR declined from 98.0 mL/min/1.73 m² at pre-LTx to 54.1 mL/min/1.73 m² at 12-weeks post-LTx. Equations based on P-Creatinine underestimated GFR decline after LTx, whereas equations based on P-Cystatin C overestimated this decline. Overall, the 2021 CKD-EPI combination equation had the lowest bias and highest precision at both pre-LTx and post-LTx. Conclusions: Caution must be applied when interpreting renal function based on equations for estimating GFR in the acute postoperative period following LTx. Simplified methods for measuring GFR may allow for more widespread use of measured GFR in this vulnerable patient population.

Health inequities and the inappropriate use of race in nephrology

Chronic kidney disease is an important clinical condition beset with racial and ethnic disparities that are associated with social inequities. Many medical schools and health centres across the USA have raised concerns about the use of race - a socio-political construct that mediates the effect of structural racism - as a fixed, measurable biological variable in the assessment of kidney disease. We discuss the role of race and racism in medicine and outline many of the concerns that have been raised by the medical and social justice communities regarding the use of race in estimated glomerular filtration rate equations, including its relationship with structural racism and racial inequities. Although race can be used to identify populations who experience racism and subsequent differential treatment, ignoring the biological and social heterogeneity within any racial group and inferring innate individual-level attributes is methodologically flawed. Therefore, although more accurate measures for estimating kidney function are under investigation, we support the use of biomarkers for determining estimated glomerular filtration rate without adjustments for race. Clinicians have a duty to recognize and elucidate the nuances of racism and its effects on health and disease. Otherwise, we risk perpetuating historical racist concepts in medicine that exacerbate health inequities and impact marginalized patient populations.

Limited Evidence for Use of a Black Race Modifier in eGFR Calculations: A Systematic Review

Background

Commonly used estimated glomerular filtration rate (eGFR) equations include a Black race modifier (BRM) that was incorporated during equation derivation. Race is a social construct, and a poorly characterized variable that is applied inconsistently in clinical settings. The BRM results in higher eGFR for any creatinine concentration, implying fundamental differences in creatinine production or excretion in Black individuals compared to other populations. Equations without inclusion of the BRM have the potential to detect kidney disease earlier in patients at the greatest risk of chronic kidney disease (CKD), but also has the potential to over-diagnose CKD or impact downstream clinical interventions. The purpose of this study was to use an evidence- based approach to systematically evaluate the literature relevant to the performance of the eGFR equations with and without the BRM and to examine the clinical impact of the use or removal.

Content

PubMed and Embase databases were searched for studies comparing measured GFR to eGFR in racially diverse adult populations using the Modification of Diet in Renal Disease or the 2009-Chronic Kidney Disease Epidemiology Collaboration-creatinine equations based on standardized creatinine measurements. Additionally, we searched for studies comparing clinical use of eGFR calculated with and without the BRM. 8,632 unique publications were identified; an additional 3 studies were added post-hoc. In total, 96 studies were subjected to further analysis and 44 studies were used to make a final assessment.

Summary

There is limited published evidence to support the use of a BRM in eGFR equations.

Evaluating the Impact and Rationale of Race-Specific Estimations of Kidney Function: Estimations from U.S. NHANES, 2015-2018

BACKGROUND

Standard equations for estimating glomerular filtration rate (eGFR) employ race multipliers, systematically inflating eGFR for Black patients. Such inflation is clinically significant because eGFR thresholds of 60, 30, and 20 ml/min/1.73m2 guide kidney disease management. Racialized adjustment of eGFR in Black Americans may thereby affect their clinical care. In this study, we analyze and extrapolate national data to assess potential impacts of the eGFR race adjustment on qualification for kidney disease diagnosis, nephrologist referral, and transplantation listing.

METHODS

Using population-representative cross-sectional data from the United States National Health and Nutrition Examination Survey (NHANES) from 2015-2018, eGFR values for Black Americans were calculated using the Modification of Diet in Renal Disease (MDRD) equation with and without the 1.21 race-specific coefficient using cohort data on age, sex, race, and serum creatinine.

FINDINGS

Without the MDRD eGFR race adjustment, 3.3 million (10.4%) more Black Americans would reach a diagnostic threshold for Stage 3 Chronic Kidney Disease, 300,000 (0.7%) more would qualify for beneficial nephrologist referral, and 31,000 (0.1%) more would become eligible for transplant evaluation and waitlist inclusion.

INTERPRETATION

These findings suggest eGFR race coefficients may contribute to racial differences in the management of kidney. We provide recommendations for addressing this issue at institutional and individual levels.

FUNDING

No external funding was received for this study.

The « race » correction in estimating glomerular filtration rate: an European point of view

PURPOSE OF REVIEW

There is currently a heated debate ongoing whether or not to use the race coefficient for black people in the Modification of Diet in Renal Diseases and Chronic Kidney Disease Epidemiology-equation. The use of the race coefficient is thought by several American authors as a source of discrimination.

RECENT FINDINGS

It has recently been shown that the race coefficient is inaccurate in European and African black people. Therefore, it seems that the race correction is more a correction for black Americans, rather than for black in general. This 'correction' at the glomerular filtration rate (GFR)-level has been criticized, as it is misleading, and should be abandoned, as it has not been shown that GFR is different between black and white people. However, as differences in creatinine generation between black and white people might exist, a correction or adjustment, different for black and white people, at the creatinine level might be required, very similar to the different scaling of creatinine for males and females.

SUMMARY

The current debate on the race coefficient is particularly difficult because of the absence of good scientific data in black subjects and there lies the real discrimination in our opinion. We therefore call for future dedicated studies, both in Europe and USA.

Age-adapted percentiles of measured glomerular filtration in healthy individuals: extrapolation to living kidney donors over 65 years

OBJECTIVES

Most data on glomerular filtration rate (GFR) originate from subjects <65 years old, complicating decision-making in elderly living kidney donors. In this retrospective multi-center study, we calculated percentiles of measured GFR (mGFR) in donors <65 years old and extrapolated these to donors ≥65 years old.

METHODS

mGFR percentiles were calculated from a development cohort of French/Belgian living kidney donors <65 years (n=1,983), using quantiles modeled as cubic splines (two linear parts joining at 40 years). Percentiles were extrapolated and validated in an internal cohort of donors ≥65 years (n=147, France) and external cohort of donors and healthy subjects ≥65 years (n=329, Germany, Sweden, Norway, France, The Netherlands) by calculating percentages within the extrapolated 5th-95th percentile (P5-P95).

RESULTS

Individuals in the development cohort had a higher mGFR (99.9 ± 16.4 vs. 86.4 ± 14 and 82.7 ± 15.5 mL/min/1.73 m²) compared to the individuals in the validation cohorts. In the internal validation cohort, none (0%) had mGFR below the extrapolated P5, 12 (8.2%) above P95 and 135 (91.8%) between P5-P95. In the external validation cohort, five subjects had mGFR below the extrapolated P5 (1.5%), 25 above P95 (7.6%) and 299 (90.9%) between P5-P95.

CONCLUSIONS

We demonstrate that extrapolation of mGFR from younger donors is possible and might aid with decision-making in elderly donors.

APOL1 Renal Risk Variants and Sickle Cell Trait Associations With Reduced Kidney Function in a Large Congolese Population-Based Study

Introduction

Methods

Results

Conclusion

Assessment of Pre-Donation Glomerular Filtration Rate: Going Back To Basics A Position Paper from the DESCARTES Working Group of the ERA-EDTA

The 2017 version of the KDIGO (Kidney Disease: Improving Global Outcomes) guidelines is the most recent international framework for the evaluation and care of living kidneys donors. Along with the call for an integrative approach evaluating the long-term end-stage kidney disease risk for the future potential donor, several recommendations are formulated regarding the predonation glomerular filtration rate (GFR) adequacy with no or little consideration for the donor candidate's age and for the importance of using reference methods of GFR measurements. Herein, we question the position of the KDIGO guidelines and discuss the rationale and modalities for a more basic, but not less demanding GFR evaluation susceptible to enable a more efficient selection of the potential kidney donor.

Calculating estimated glomerular filtration rate without the race correction factor: Observations at a large academic medical system

BACKGROUND AND AIMS

Creatinine-based MDRD and CKD-EPI equations include a race correction factor, which results in higher eGFR in Black patients. We evaluated the impact on our patient population upon adoption of the CKD-EPI equation and the removal of the race correction factor from the equation.

MATERIALS AND METHODS

Retrospective analysis of blood creatinine results and respective eGFR values calculated by the MDRD or CKD-EPI equation without the race correction factor (CKD-EPINoRace) in a large academic medical system over a 20.5-month period.

RESULTS

In our population, when changing from MDRD to CKD-EPINoRace, we observed that 3.5% of all patients were reclassified to categorically have worse kidney function. However, we also observed fewer patients overall with eGFR below 60 mL/min/1.73 m2. Around 60 and 20 mL/min/1.73 m2, 2.96% and 0.16% of all patients > 65 years of age were reclassified, as were 4.29% and 0.03% of all Black patients, respectively. When calculated with CKD-EPINoRace, median eGFR was not meaningfully different between Black and non-Black patients (p = 0.02).

CONCLUSIONS

Changing from MDRD to CKD-EPINoRace could lead to a lower referral rate to nephrology. The distributions of creatinine and eGFR calculated with CKD-EPINoRace were not meaningfully different in Black and non-Black patients.

Prospective Comparison of 24-Hour Urine Creatinine Clearance with Estimated Glomerular Filtration Rates in Chronic Renal Disease Patients of African Descent

BACKGROUND

The 24-hour (24-h) creatinine clearance (CrCl) is the most common method for measuring GFR in clinical laboratories. However, the limitations of CrCl have resulted in the widespread acceptance of mathematically derived estimated glomerular filtration rate (eGFR) using Cockcroft-Gault (CG), Modification of Diet in Renal Disease (MDRD) and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in predicting eGFR. The aim of the study was to compare 24-h CrCl with eGFR derived from these formulae and to identify which could be the best alternative.

METHOD

A prospective study was conducted involving 140 CKD patients. Creatinine and cystatin C concentrations were determined using the cobas 6000 analyzer. The eGFR was calculated using the CG formula, 4-variable MDRD and CKD-EPI equations, and Bland-Alman plots bias was determined.

RESULTS

The CG and MDRD formulas had mean eGFR values similar to CrCl and correlation coefficients (r) were highest for CG (0.906) and lowest for MDRD (0.799). The CG equation was in agreement with 24-h CrCl in all but stage V CKD while the MDRD equation compared well in all except Stage IV CKD. The CG equation was positively biased (0.9857) while the MDRD had a negative bias (-0.05).

CONCLUSION

The Cockcroft-Gault formula provides a more accurate assessment of GFR than 24-h CrCl and would be recommended as a substitute to provide the best estimate of GFR in our population.

Association Between Deceased Donor Acute Kidney Injury Assessed Using Baseline Serum Creatinine Back-Estimation and Graft Survival: Results From the French National CRISTAL Registry

RATIONALE & OBJECTIVE

Deceased donor acute kidney injury (AKI) frequently leads to kidney discards, but its impact on long-term graft survival in kidney transplant recipients remains unclear. We investigated the association between deceased donor AKI assessed using back-estimation of baseline serum creatinine (Scr) and graft survival.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

Adult patients represented within the French CRISTAL registry who received a single kidney allograft from brain-dead deceased donors between January 2006 and December 2017.

EXPOSURE

A back-estimated Scr baseline value was derived for an assumed glomerular filtration rate at 75mL/min/1.73m², using the MDRD Study equation. A refined classification system for donor AKI was implemented as follows: no AKI, undetermined AKI/chronic kidney disease (CKD), recovery from AKI, and ongoing AKI.

OUTCOME

Death-censored graft survival.

ANALYTICAL APPROACH

Multivariable Cox models using a robust variance estimator for paired kidneys from the same donor.

RESULTS

We classified 26,786 recipients as follows: no AKI (n=19,276); undetermined AKI/CKD (n=1,745); recovery from AKI (n=2,392); and ongoing AKI (n=3,373). We observed 4,458 kidney graft losses during a median follow-up period of 5.7 years. Compared with no AKI, ongoing AKI was associated with an increased risk of graft failure (hazard ratio [HR], 1.24 [95% CI, 1.13-1.35]). The HRs for graft failure in the undetermined AKI/CKD and recovery from AKI groups (1.22 [95% CI, 1.07-1.38] and 1.18 [95% CI, 1.06-1.31], respectively) were similar to those observed in the ongoing AKI group. The adverse effect of deceased donor AKI was no longer evident when relying either on the admission or the lowest Scr throughout the procurement procedure as baseline Scr.

LIMITATIONS

No measurement of urine output in donors.

CONCLUSIONS

Deceased donor ongoing AKI, undetermined AKI/CKD, and recovery from AKI according to back-estimated baseline Scr are associated with decreased graft survival. The definition of baseline Scr as the first value measured on admission would have led to a misclassification bias and erroneous estimates.

Assessment of kidney function: clinical indications for measured GFR

In the vast majority of cases, glomerular filtration rate (GFR) is estimated using serum creatinine, which is highly influenced by age, sex, muscle mass, body composition, severe chronic illness and many other factors. This often leads to misclassification of patients or potentially puts patients at risk for inappropriate clinical decisions. Possible solutions are the use of cystatin C as an alternative endogenous marker or performing direct measurement of GFR using an exogenous marker such as iohexol. The purpose of this review is to highlight clinical scenarios and conditions such as extreme body composition, Black race, disagreement between creatinine- and cystatin C-based estimated GFR (eGFR), drug dosing, liver cirrhosis, advanced chronic kidney disease and the transition to kidney replacement therapy, non-kidney solid organ transplant recipients and living kidney donors where creatinine-based GFR estimation may be invalid. In contrast to the majority of literature on measured GFR (mGFR), this review does not include aspects of mGFR for research or public health settings but aims to reach practicing clinicians and raise their understanding of the substantial limitations of creatinine. While including cystatin C as a renal biomarker in GFR estimating equations has been shown to increase the accuracy of the GFR estimate, there are also limitations to eGFR based on cystatin C alone or the combination of creatinine and cystatin C in the clinical scenarios described above that can be overcome by measuring GFR with an exogenous marker. We acknowledge that mGFR is not readily available in many centres but hope that this review will highlight and promote the expansion of kidney function diagnostics using standardized mGFR procedures as an important milestone towards more accurate and personalized medicine.

Impact of rural versus urban setting on kidney markers: a cross-sectional study in South-Kivu, DRCongo

Background

Most studies of chronic kidney disease (CKD) in Sub-Saharan Africa (SSA) have been conducted in urban settings. They relied on GFR estimated from serum creatinine alone and on the inexpensive, convenient urinary dipstick to assess proteinuria. The dipstick for proteinuria has not been directly compared with the gold standard albumin-to-creatinine ratio (ACR) in a large-sized study in SSA. We hereby assessed the influence of rural versus urban location on the level, interpretation, and diagnostic performance of proteinuria dipstick versus ACR.

Methods

In a cross-sectional population-based study of CKD in both urban (n = 587) and rural (n = 730) settings in South-Kivu, Democratic Republic of Congo (DRC), we assessed the prevalence, performance (sensitivity, specificity, positive predictive value and negative predictive value) and determinants of a positive dipstick proteinuria as compared with albuminuria (ACR). Albuminuria was subdivided into: A1 (< 30 mg/g creatinine), A2 (30 to 299 mg/g creatinine) and A3 (≥ 300 mg/g creatinine).

Results

The overall prevalence of positive dipstick proteinuria (≥ 1+) was 9.6 % (95 % CI, 7.9–11.3) and was higher in rural than in urban residents (13.1 % vs. 4.8 %, p < 0.001), whereas the prevalence of albuminuria (A2 or A3) was similar in both sites (6 % rural vs. 7.6 % urban, p = 0.31). In both sites, dipstick proteinuria ≥ 1 + had a poor sensitivity (< 50 %) and positive predictive value (< 11 %) for the detection of A2 or A3. The negative predictive value was 95 %. Diabetes [aOR 6.12 (1.52–24.53)] was a significant predictor of A3 whereas alkaline [aOR 7.45 (3.28–16.93)] and diluted urine [aOR 2.19 (1.35–3.57)] were the main predictors of positive dipstick proteinuria.

Conclusions

ACR and dipstick proteinuria have similar positivity rates in the urban site whereas, in the rural site, dipstick was 2-fold more often positive than ACR. The poor sensitivity and positive predictive value of the dipstick as compared with ACR makes it unattractive as a screening tool in community studies of CKD in SSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02431-w.

A New Panel-Estimated GFR, Including β2-Microglobulin and β-Trace Protein and Not Including Race, Developed in a Diverse Population

RATIONALE AND OBJECTIVE

Glomerular filtration rate (GFR) estimation based on creatinine and cystatin C (eGFRcr-cys) is more accurate than estimated GFR (eGFR) based on creatinine or cystatin C alone (eGFRcr or eGFRcys, respectively), but the inclusion of creatinine in eGFRcr-cys requires specification of a person's race. β2-Microglobulin (B2M) and β-trace protein (BTP) are alternative filtration markers that appear to be less influenced by race than creatinine is.

STUDY DESIGN

Study of diagnostic test accuracy.

SETTING AND PARTICIPANTS

Development in a pooled population of 7 studies with 5,017 participants with and without chronic kidney disease. External validation in a pooled population of 7 other studies with 2,245 participants.

TESTS COMPARED

Panel eGFR using B2M and BTP in addition to cystatin C (3-marker panel) or creatinine and cystatin C (4-marker panel) with and without age and sex or race.

OUTCOMES

GFR measured as the urinary clearance of iothalamate, plasma clearance of iohexol, or plasma clearance of [51Cr]EDTA.

RESULTS

Mean measured GFRs were 58.1 and 83.2 mL/min/1.73 m2, and the proportions of Black participants were 38.6% and 24.0%, in the development and validation populations, respectively. In development, addition of age and sex improved the performance of all equations compared with equations without age and sex, but addition of race did not further improve the performance. In validation, the 4-marker panels were more accurate than the 3-marker panels (P < 0.001). The 3-marker panel without race was more accurate than eGFRcys (percentage of estimates greater than 30% different from measured GFR [1 - P30] of 15.6% vs 17.4%; P = 0.01), and the 4-marker panel without race was as accurate as eGFRcr-cys (1 - P30 of 8.6% vs 9.4%; P = 0.2). Results were generally consistent across subgroups.

LIMITATIONS

No representation of participants with severe comorbid illness and from geographic areas outside of North America and Europe.

CONCLUSIONS

The 4-marker panel eGFR is as accurate as eGFRcr-cys without requiring specification of race. A more accurate race-free eGFR could be an important advance.

[Nephrology in Sub-saharan Africa: Past, present, future]

Nephrology was a relatively poorly known specialty in sub-Saharan Africa until the early 1980s, because of low awareness and lack of access to diagnosis and renal replacement therapies. Nephrology has seen progress on the continent despite an unfavourable economic and geopolitical environment. With a prevalence of fewer than five nephrologists per million inhabitants, the training of nephrologists, now carried out on the continent, allowed to have more than 200 specialists trained in the last decade in French-speaking sub-Saharan Africa. Clinical and basic research is developing with quality work published from the continent in major international journals. The population receiving haemodialysis remains small, between 0 and 200 per million inhabitants. Kidney transplantation, with a prevalence between 0 and 5 per million inhabitants, is only well structured in South Africa. In this context of scarce resources, a strategy based on the prevention of non-communicable diseases in general, and chronic kidney disease in particular, should be prioritised.

Performance and Determinants of Serum Creatinine and Cystatin C-Based GFR Estimating Equations in South Asians

INTRODUCTION

The creatinine-based Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) estimated glomerular filtration rate (eGFR) equation was calibrated for the general Pakistan population (eGFRcr-PK) to eliminate bias and improve accuracy. Cystatin C-based CKD-EPI equations (eGFRcys and eGFRcr-cys) have not been assessed in this population, and non-GFR determinants of cystatin C are unknown.

METHODS

We assessed eGFRcys, eGFRcr-cys, and non-GFR determinants of cystatin C in a cross-sectional study of 557 participants (≥40 years of age) from Pakistan. We compared bias (median difference in measured GFR [mGFR] and eGFR), precision (interquartile range [IQR] of differences), accuracy (percentage of eGFR within 30% of mGFR), root mean square error (RMSE), and classification of mGFR <60 ml/min/1.73 m2 (area under the receiver operating characteristic curve [AUC] and net reclassification index [NRI]) among eGFR equations.

RESULTS

We found that eGFRcys underestimated mGFR (bias, 12.7 ml/min/1.73 m2 [95% confidence interval {CI} 10.7-15.2]). eGFRcr-cys did not improve performance over eGFRcr-PK in precision (P = 0.52), accuracy (P = 0.58), or RMSE (P = 0.49). Results were consistent among subgroups by age, sex, smoking, body mass index (BMI), and eGFR. NRI was 7.31% (95% CI 1.52%-13.1%; P < 0.001) for eGFRcr-cys versus eGFRcr-PK, but AUC was not improved (0.92 [95% CI 0.87-0.96] vs. 0.90 [95% CI 0.86-0.95]; P = 0.056). Non-GFR determinants of higher cystatin C included male sex, smoking, higher BMI and total body fat, and lower lean body mass.

CONCLUSION

eGFRcys underestimated mGFR in South Asians and eGFRcr-cys did not offer substantial advantage compared with eGFRcr-PK. Future studies are warranted to better understand the large bias in eGFRcys and non-GFR determinants of cystatin C in South Asians.

Evaluating chronic kidney disease in rural South Africa: comparing estimated glomerular filtration rate using point-of-care creatinine to iohexol measured GFR

OBJECTIVES

The prevalence of chronic kidney disease is rising rapidly in low- and middle-income countries. Serum creatinine and estimation of glomerular filtration rate (GFR) are critical diagnostic tools, yet access to centralised laboratory services remains limited in primary care resource-limited settings. The aim of this study was to evaluate point-of-care (POC) technologies for serum creatinine measurement and to compare their performance to a gold standard measurement using iohexol measured GFR (mGFR).

METHODS

POC creatinine was measured using iSTAT^® and StatSensor^® devices in capillary and venous whole blood, and laboratory creatinine was measured using the compensated kinetic Jaffe method in 670 participants from a rural area in South Africa. GFR estimating equations Chronic Kidney Disease Epidemiology Collaboration and Modification of Diet in Renal Disease (CKD-EPI and MDRD) for POC and laboratory creatinine were compared to iohexol mGFR.

RESULTS

Calculated GFR for laboratory and POC creatinine measurements overestimated GFR (positive bias of 1.9-34.1 mL/min/1.73 m²). However, all POC devices had less positive bias than the laboratory Jaffe method (1.9-14.7 vs. 34.1 for MDRD, and 8.4-19.9 vs. 28.6 for CKD-EPI). Accuracy within 30% of mGFR ranged from 0.56 to 0.72 for POC devices and from 0.36 to 0.43 for the laboratory Jaffe method. POC devices showed wider imprecision with coefficients of variation ranging from 4.6 to 10.2% compared to 3.5% for the laboratory Jaffe method.

CONCLUSIONS

POC estimated GFR (eGFR) showed improved performance over laboratory Jaffe eGFR, however POC devices suffered from imprecision and large bias. The laboratory Jaffe method performed poorly, highlighting the need for laboratories to move to enzymatic methods to measure creatinine.

Estimated glomerular filtration rate in children: adapting existing equations for a specific population

BACKGROUND

Creatinine-based glomerular filtration rate (GFR)-estimating equations frequently do not perform well in populations that differ from the development populations in terms of mean GFR, age, pathology, ethnicity, and diet. After first evaluating the performance of existing equations, the aim of this study was to demonstrate the utility of an in-house modification of the equations to better fit a specific population.

METHODS

Estimated GFR using 8 creatinine-based equations was first compared to 2-sample ⁵¹Cr-ethylenediaminetetra-acetic acid plasma clearance in non-cancer and cancer groups independently. The groups were then divided into development and validation sets. Using the development set data, the Microsoft® Excel SOLVER add-in was used to modify the parameters of 7 equations to better fit the data. Using the validation set data, the performance of the original and modified equations was compared.

RESULTS

Two hundred fifty-six GFR measurements were performed in 160 children. GFR was overestimated in both groups (non-cancer 4.3-22.6 ml/min/1.73 m², cancer 17.2-46.6 ml/min/1.73 m²). The root mean square error (RMSE) was 19.1-21.8 ml/min/1.73 m² (non-cancer) and 18.6-20.8 ml/min/1.73 m² (cancer). The P₃₀ values were 49.1-73.0% (non-cancer) and 19.6-66.0% (cancer). Modifying the parameters of seven equations resulted in significant improvements in the P₃₀ values in the non-cancer (65.0-85.0%) and cancer (79.6-87.8%) groups.

CONCLUSIONS

Modifying the parameters of pediatric GFR estimating-equations using a simple Excel-based tool significantly improved their accuracy in both non-cancer and cancer populations. Graphical abstract.