How best to estimate glomerular filtration rate? Novel filtration markers and their application

Efficacy of parsley seed-supplemented bread in improving serum osteopontin level and renal health in obese women: A nutritional intervention study

BACKGROUND

Obesity is a global epidemic and a major contributor to chronic kidney disease worldwide. This interventional study aimed to evaluate the effects of a unique parsley seed bread and a healthy balanced diet on serum osteopontin level and renal function in obese women.

METHODS

A total of 85 obese women (BMI, 35.68 ± 0.47 kg/m2) participated in an 8-week nutritional intervention comprising two phases. In the first phase, participants consumed 100 g of ground parsley seed bread along with a healthy balanced low caloric regimen for four weeks. In the second phase, Baladi bread was substituted for the supplement, providing an equal caloric intake, for another four weeks. Relevant Anthropometric measurements, blood pressure, dietary recall, and biochemical parameters (osteopontin, IL-1β, IL-10, kidney functions, and lipid parameters) were assessed before and after each intervention phase.

RESULTS

Following the initial intervention phase, there were significant improvements in all recorded mean anthropometric parameters (p ≤ 0.001). Lipid parameters and risk factors also significantly decreased (p < 0.05), while osteopontin, creatinine, and IL-1β levels decreased significantly. eGFR, creatinine clearance, IL-10 increased. However, these improved values returned to elevated levels after the omission of the supplement in the second phase. There was a significant negative correlation between osteopontin and creatinine, creatinine clearance, and IL-10.

CONCLUSION

The combined effect of the novel parsley seed-based intervention and a healthy balanced low-calorie regimen demonstrated improvements in osteopontin level associated with renal disorders, and inflammation, in addition to dyslipidemia in obese women. This suggests a promising approach for improving and protecting kidney disorders.

β-Trace Protein and β2-Microglobulin do not Improve Estimation of Glomerular Filtration Rate in Kidney Transplant Recipients Compared With Creatinine and Cystatin C

BACKGROUND

Reliable estimates of glomerular filtration rate (eGFR) are important for detecting changes in graft function in kidney transplant recipients. Current eGFR equations are based on plasma creatinine and/or cystatin C; however, these are associated with significant bias. This study investigated if equations based on β-trace protein (BTP) and β2-microglobulin (B2M) performed better than the 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations based on creatinine and cystatin C among kidney transplant recipients.

METHODS

We included samples and data from the clinical trial CONTEXT. Glomerular filtration rate (GFR) was measured by plasma clearance of an exogenous marker. The eGFR was calculated using the CKD-EPI equations for estimating GFR from BTP and/or B2M and the 2021 CKD-EPI creatinine and creatinine-cystatin C equations. The GFR estimates were evaluated 3 (n = 82) and 12 (n = 64) months after transplant using mean bias, precision, and accuracy. Furthermore, we analyzed the ability of the equations to correctly classify the direction of changes in measured GFR from 3 to 12 months.

RESULTS

Among the BTP- and B2M-based equations, the combined eGFR-BTP-B2M performed best with respect to precision (SD = 7.64 mL/min/1.73 m2) and accuracy (±10% from measured GFR = 36%). The eGFR-BTP-B2M and the eGFR-creatinine-cystatin C (2021) performed similarly when comparing precision, accuracy, and residuals (P = .481). The BTP- and/or B2M-based equations did not perform better than the eGFR-creatinine-cystatin C (2021) in correctly classifying the direction of changes in measured GFR from 3 to 12 months.

CONCLUSIONS

β-trace protein and/or B2M do not improve the estimation of GFR when compared with creatinine- and cystatin C-based 2021 CKD-EPI equations.

Performance of Nuclear Magnetic Resonance-Based Estimated Glomerular Filtration Rate in a Real-World Setting

An accurate estimate of glomerular filtration rate (eGFR) is essential for proper clinical management, especially in patients with kidney dysfunction. This prospective observational study evaluated the real-world performance of the nuclear magnetic resonance (NMR)-based GFR_NMR equation, which combines creatinine, cystatin C, valine, and myo-inositol with age and sex. We compared GFR_NMR performance to that of the 2021 CKD-EPI creatinine and creatinine-cystatin C equations (CKD-EPI_2021Cr and CKD-EPI_2021CrCys), using 115 fresh routine samples of patients scheduled for urinary iothalamate clearance measurement (mGFR). Median bias to mGFR of the three eGFR equations was comparably low, ranging from 0.4 to 2.0 mL/min/1.73 m². GFR_NMR outperformed the 2021 CKD-EPI equations in terms of precision (interquartile range to mGFR of 10.5 vs. 17.9 mL/min/1.73 m² for GFR_NMR vs. CKD-EPI_2021CrCys; p = 0.01) and accuracy (P15, P20, and P30 of 66.1% vs. 48.7% [p = 0.007], 80.0% vs. 60.0% [p < 0.001] and 95.7% vs. 86.1% [p = 0.006], respectively, for GFR_NMR vs. CKD-EPI_2021CrCys). Clinical parameters such as etiology, comorbidities, or medications did not significantly alter the performance of the three eGFR equations. Altogether, this study confirmed the utility of GFR_NMR for accurate GFR estimation, and its potential value in routine clinical practice for improved medical care.

Investigation of N,N,N-Trimethyl-L-alanyl-L-proline Betaine (TMAP) as a Biomarker of Kidney Function

Glomerular filtration rate (GFR) is the most widely used tool for the measurement of kidney function, but endogenous biomarkers such as cystatin C and creatinine have limitations. A previous metabolomic study revealed N,N,N-trimethyl-L-alanyl-L-proline betaine (TMAP) to be reflective of kidney function. In this study, we developed a quantitative LCMS assay for the measurement of TMAP and evaluated TMAP as a biomarker of GFR. An assay to measure TMAP was developed using liquid chromatography-mass spectrometry. After validation of the method, we applied it to plasma samples from three distinct kidney disease patient cohorts: nondialysis chronic kidney disease (CKD) patients, patients receiving peritoneal and hemodialysis, and living kidney donors. We investigated whether TMAP was conserved in other mammalian and nonmammalian species, by analyzing plasma samples from Wistar rats with diet-induced CKD and searching for putative matches to the m/z for TMAP and its known fragments in the raw sample data repository "Metabolomics Workbench". The assay can measure plasma TMAP at a lower limit of quantitation (100 ng/mL) with an interday precision and accuracy of 12.8 and 12.1%, respectively. In all three patient cohorts, TMAP concentrations are significantly higher in patients with CKD than in controls with a normal GFR. Further, TMAP concentrations are also elevated in rats with CKD and TMAP is present in the sap produced from Acer saccharum trees. TMAP concentration is inversely related to GFR suggesting that it is a marker of kidney function. TMAP is present in nonmammalian species suggesting that it is part of a biologically conserved process.

Construct a classification decision tree model to select the optimal equation for estimating glomerular filtration rate and estimate it more accurately

Chronic kidney disease (CKD) has become a worldwide public health problem and accurate assessment of renal function in CKD patients is important for the treatment. Although the glomerular filtration rate (GFR) can accurately evaluate the renal function, the procedure of measurement is complicated. Therefore, endogenous markers are often chosen to estimate GFR indirectly. However, the accuracy of the equations for estimating GFR is not optimistic. To estimate GFR more precisely, we constructed a classification decision tree model to select the most befitting GFR estimation equation for CKD patients. By searching the HIS system of the First Affiliated Hospital of Zhejiang Chinese Medicine University for all CKD patients who visited the hospital from December 1, 2018 to December 1, 2021 and underwent Gate's method of ^99mTc-DTPA renal dynamic imaging to detect GFR, we eventually collected 518 eligible subjects, who were randomly divided into a training set (70%, 362) and a test set (30%, 156). Then, we used the training set data to build a classification decision tree model that would choose the most accurate equation from the four equations of BIS-2, CKD-EPI(CysC), CKD-EPI(Cr-CysC) and Ruijin, and the equation was selected by the model to estimate GFR. Next, we utilized the test set data to verify our tree model, and compared the GFR estimated by the tree model with other 13 equations. Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and Bland-Altman plot were used to evaluate the accuracy of the estimates by different methods. A classification decision tree model, including BSA, BMI, 24-hour Urine protein quantity, diabetic nephropathy, age and RASi, was eventually retrieved. In the test set, the RMSE and MAE of GFR estimated by the classification decision tree model were 12.2 and 8.5 respectively, which were lower than other GFR estimation equations. According to Bland-Altman plot of patients in the test set, the eGFR was calculated based on this model and had the smallest degree of variation. We applied the classification decision tree model to select an appropriate GFR estimation equation for CKD patients, and the final GFR estimation was based on the model selection results, which provided us with greater accuracy in GFR estimation.

Analytical Validation of GFRNMR: A Blood-Based Multiple Biomarker Assay for Accurate Estimation of Glomerular Filtration Rate

Accurate and precise monitoring of kidney function is critical for a timely and reliable diagnosis of chronic kidney disease (CKD). The determination of kidney function usually involves the estimation of the glomerular filtration rate (eGFR). We recently reported the clinical performance of a new eGFR equation (GFR_NMR) based on the nuclear magnetic resonance (NMR) measurement of serum myo-inositol, valine, and creatinine, in addition to the immunoturbidometric quantification of serum cystatin C, age and sex. We now describe the analytical performance evaluation of GFR_NMR according to the Clinical and Laboratory Standards Institute guidelines. Within-laboratory coefficients of variation (CV%) of the GFR_NMR equation did not exceed 4.3%, with a maximum CV% for repeatability of 3.7%. Between-site reproducibility (three sites) demonstrated a maximum CV% of 5.9%. GFR_NMR stability was demonstrated for sera stored for up to 8 days at 2–10°C and for NMR samples stored for up to 10 days in the NMR device at 6 ± 2°C. Substance interference was limited to 4/40 (10.0%) of the investigated substances, resulting in an underestimated GFR_NMR (for glucose and metformin) or a loss of results (for naproxen and ribavirin) for concentrations twice as high as usual clinical doses. The analytical performances of GFR_NMR, combined with its previously reported clinical performance, support the potential integration of this NMR method into clinical practice.

Association Between Low-Level Blood Cadmium Exposure and Hyperuricemia in the American General Population: a Cross-sectional Study

Heavy metals, including cadmium, are suspected to increase serum uric acid levels and hyperuricemia in both gender, but the evidences about this are inconclusive. To determine whether serum cadmium in American adults(≥19 years old) is associated with uric acid levels and risk of hyperuricemia, 2620 participants from the US National Health and Nutrition Examination Survey were recruited. Hyperuricemia was defined as a serum UA concentration ≥ 416.4 μmol/L for men and ≥ 356.9 μmol/L for women. Regression analyses were used to analyze the association of cadmium with serum UA and hyperuricemia. The threshold effect explored using two-piecewise linear regression model by the smoothing plot. The overall median of blood cadmium was 0.27 μg/L in men and 0.33μg/L in women. After adjusting for the covariates (race; age; education; BMI; smoke status; alcohol consumption; blood lead; hypertension; diabetes mellitus; hemoglobin; eGFR; triglyceride; and cholesterol), a non-linear relationship between hyperuricemia and cadmium among men was detected; and there was a positive line correlation between them for women (OR = 1.58; 95%CI (1.08, 2.31)). No significant association between uric acid and cadmium in either gender was found. Blood cadmium levels in the range currently considered acceptable were positively associated with increased prevalence of hyperuricemia in women, but inversely associated in men (cadmium <0.77μg/L).

Estimating Glomerular Filtration Rate from Serum Myo-Inositol, Valine, Creatinine and Cystatin C

Assessment of renal function relies on the estimation of the glomerular filtration rate (eGFR). Existing eGFR equations, usually based on serum levels of creatinine and/or cystatin C, are not uniformly accurate across patient populations. In the present study, we expanded a recent proof-of-concept approach to optimize an eGFR equation targeting the adult population with and without chronic kidney disease (CKD), based on a nuclear magnetic resonance spectroscopy (NMR) derived 'metabolite constellation' (GFRNMR). A total of 1855 serum samples were partitioned into development, internal validation and external validation datasets. The new GFRNMR equation used serum myo-inositol, valine, creatinine and cystatin C plus age and sex. GFRNMR had a lower bias to tracer measured GFR (mGFR) than existing eGFR equations, with a median bias (95% confidence interval [CI]) of 0.0 (-1.0; 1.0) mL/min/1.73 m2 for GFRNMR vs. -6.0 (-7.0; -5.0) mL/min/1.73 m2 for the Chronic Kidney Disease Epidemiology Collaboration equation that combines creatinine and cystatin C (CKD-EPI2012) (p < 0.0001). Accuracy (95% CI) within 15% of mGFR (1-P15) was 38.8% (34.3; 42.5) for GFRNMR vs. 47.3% (43.2; 51.5) for CKD-EPI2012 (p < 0.010). Thus, GFRNMR holds promise as an alternative way to assess eGFR with superior accuracy in adult patients with and without CKD.

Design and methodology of the chronic kidney disease as a dysmetabolic determinant of disability among older people (CKD-3D) study: a multicenter cohort observational study

Background

Chronic kidney disease (CKD) is a common condition in older people and represents a global health issue since it increases the risk of associated comorbidities and all-cause mortality. Furthermore, older people with reduced renal function might be at higher risk for developing functional limitation and disability. Moreover, the current creatinine-based measures of renal function are influenced by several factors in older population. The aims of the CKD-3D project are to perform an observational study to expand the knowledge about CKD-disability relationship and to investigate the use of novel biomarkers of kidney function.

Methods

An observational, multicenter, prospective cohort study will be conducted in 75 + old patients consecutively admitted to acute care wards of geriatric medicine at participating hospitals. The study planned to enroll 440 patients undergoing clinical and laboratory evaluations at baseline and after 12 months. Face-to-face follow-up at 6 months and telephone follow-up at 3 and 9 months will be carried out. Comprehensive Geriatric Assessment (CGA) and the measurement of Cystatin C, Beta-Trace Protein and Beta2-Microglobulin levels will be included.

Discussion

This study will provide useful information to prevent CKD-related disability by collecting real-life data over 1-year period. The combined approach of CGA and the investigation of innovative existing biomarkers will make it possible to develop new recommendations and guidelines for a patient-centered approach. It is believed that such a study may lead to an improvement of knowledge on CKD in elderly patients and may also have implications in daily clinical practice and in decision-making process.

Choosing an appropriate glomerular filtration rate estimating equation: role of body mass index

Background

We aimed to investigate the accuracy of different equations in evaluating estimated glomerular filtration rate (eGFR) in a Chinese population with different BMI levels.

Methods

A total of 837 Chinese patients were enrolled, and the eGFRs were calculated by three Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations, three full-age spectrum (FAS) equations and two Modification of Diet in Renal Disease (MDRD) equations. Results of measured GFR (mGFR) by the 99Tcm-diathylenetriamine pentaacetic acid (99Tcm-DTPA) renal dynamic imaging method were the reference standards. According to BMI distribution, the patients were divided into three intervals: below 25th(BMI_P25), 25th to 75th(BMI_P25–75) and over 75th percentiles (BMI_P75).

Results

The medium BMI of the three BMI intervals were 20.9, 24.8 and 28.9 kg/m², respectively. All deviations from mGFR (eGFR) were correlated with BMI (p < 0.05). The percentage of cases in which eGFR was within mGFR ±30% (P30) was used to represent the accuracy of each equation. Overall, eGFR_{FAS_Cr_CysC} and eGFREPI_Cr_2009 performed similarly, showing the best agreement with mGFR among the eight equations in Bland-Altman analysis (biases: 4.1 and − 4.2 mL/min/1.73m², respectively). In BMI_P25 interval, eGFR_{FAS_Cr} got − 0.7 of the biases with 74.2% of P30, the kappa value was 0.422 in classification of CKD stages and the AUC₆₀ was 0.928 in predicting renal insufficiency, and eGFREPI_Cr_2009 got 2.3 of the biases with 71.8% of P30, the kappa value was 0.418 in classification of CKD stages and the AUC₆₀ was 0.920 in predicting renal insufficiency. In BMI_P25–75 interval, the bias of eGFR_{FAS_Cr_CysC} was 4.0 with 85.0% of P30, the kappa value was 0.501 and the AUC₆₀ was 0.941, and eGFR_{FAS_Cr_CysC} showed balanced recognition ability of each stage of CKD (62.3, 63.7, 68.0, 71.4 and 83.3% respectively). In BMI_P75 interval, the bias of eGFR_{EPI_Cr_CysC_2012} was 3.8 with 78.9% of P30, the kappa value was 0.484 the AUC₆₀ was 0.919, and eGFR_{EPI_Cr_CysC_2012} equation showed balanced and accurate recognition ability of each stage (60.5, 60.0, 71.4, 57.1 and 100% respectively). In BMI_P75 interval, the bias of eGFR_{FAS_Cr_CysC} was − 1.8 with 78.5% of P30, the kappa value was 0.485, the AUC₆₀ was 0.922. However, the recognition ability of each stage of eGFR_{FAS_Cr_CysC} eq. (71.1, 61.2, 70.0, 42.9 and 50.0% respectively) was not as good as GFR_{EPI_Cr_CysC_2012} equation.

Conclusion

For a Chinese population, we tend to recommend choosing eGFR_{FAS_Cr} and eGFR_{EPI_Cr_2009} when BMI was around 20.9, eGFR_{FAS_Cr_CysC} when BMI was near 24.8, and eGFR_{EPI_Cr_CysC_2012} when BMI was about 28.9.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02395-x.

A Review of Specific Biomarkers of Chronic Renal Injury and Their Potential Application in Nonclinical Safety Assessment Studies

A host of novel renal biomarkers have been developed over the past few decades which have enhanced monitoring of renal disease and drug-induced kidney injury in both preclinical studies and in humans. Since chronic kidney disease (CKD) and acute kidney injury (AKI) share similar underlying mechanisms and the tubulointerstitial compartment has a functional role in the progression of CKD, urinary biomarkers of AKI may provide predictive information in chronic renal disease. Numerous studies have explored whether the recent AKI biomarkers could improve upon the standard clinical biomarkers, estimated glomerular filtration rate (eGFR), and urinary albumin to creatinine ratio, for predicting outcomes in CKD patients. This review is an introduction to alternative assays that can be utilized in chronic (>3 months duration) nonclinical safety studies to provide information on renal dysfunction and to demonstrate specific situations where these assays could be utilized in nonclinical drug development. Novel biomarkers such as symmetrical dimethyl arginine, dickkopf homolog 3, and cystatin C predict chronic renal injury in animals, act as surrogates for GFR, and may predict changes in GFR in patients over time, ultimately providing a bridge from preclinical to clinical renal monitoring.

Serum Myo-Inositol, Dimethyl Sulfone, and Valine in Combination with Creatinine Allow Accurate Assessment of Renal Insufficiency-A Proof of Concept

Evaluation of renal dysfunction includes estimation of glomerular filtration rate (eGFR) as the initial step and subsequent laboratory testing. We hypothesized that combined analysis of serum creatinine, myo-inositol, dimethyl sulfone, and valine would allow both assessment of renal dysfunction and precise GFR estimation. Bio-banked sera were analyzed using nuclear magnetic resonance spectroscopy (NMR). The metabolites were combined into a metabolite constellation (GFRNMR) using n = 95 training samples and tested in n = 189 independent samples. Tracer-measured GFR (mGFR) served as a reference. GFRNMR was compared to eGFR based on serum creatinine (eGFRCrea and eGFREKFC), cystatin C (eGFRCys-C), and their combination (eGFRCrea-Cys-C) when available. The renal biomarkers provided insights into individual renal and metabolic dysfunction profiles in selected mGFR-matched patients with otherwise homogenous clinical etiology. GFRNMR correlated better with mGFR (Pearson correlation coefficient r = 0.84 vs. 0.79 and 0.80). Overall percentages of eGFR values within 30% of mGFR for GFRNMR matched or exceeded those for eGFRCrea and eGFREKFC (81% vs. 64% and 74%), eGFRCys-C (81% vs. 72%), and eGFRCrea-Cys-C (81% vs. 81%). GFRNMR was independent of patients' age and sex. The metabolite-based NMR approach combined metabolic characterization of renal dysfunction with precise GFR estimation in pediatric and adult patients in a single analytical step.

Predictive value of cystatin C and neutrophil gelatinase-associated lipocalin in contrast-induced nephropathy: A meta-analysis

Background

There are still limited studies comprehensively examining the diagnostic performance of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C in contrast-induced nephropathy (CIN). The study aimed to investigate and compare the predictive value of NGAL and cystatin C in the early diagnosis of CIN.

Methods and materials

We searched the PubMed, EMBASE and Cochrane Library databases until November 10, 2019. The methodological quality of the included studies was assessed by the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool. Bivariate modeling and hierarchical summary receiver operating characteristic (HSROC) modeling were performed to summarize and compare the diagnostic performance of blood/urine NGAL and serum cystatin C in CIN. Subgroup and meta-regression analyses were performed according to the study and patient characteristics.

Results

Thirty-seven studies from thirty-one original studies were included (blood NGAL, 1840 patients in 9 studies; urine NGAL, 1701 patients in 10 studies; serum cystatin C, 5509 patients in 18 studies). Overall, serum cystatin C performed better than serum/urine NGAL (pooled DOR: 43 (95%CI: 12–152); AUROC: 0.93; λ: 3.79); serum and urine NGAL had a similar diagnostic performance (pooled DOR: 25 (95%CI: 6–108)/22(95%CI: 8–64); AUROC: 0.90/0.89; λ: 3.20/3.08). Meta-regression analysis indicated that the sources of heterogeneity might be CIN definition, assays, and nationalities.

Conclusion

Both NGAL and cystatin C can serve as early diagnostic indicators of CIN, while cystatin C may perform better than NGAL.

The inverse association of glomerular function and urinary β2-MG excretion and its implications for cadmium health risk assessment

Urinary β2-microgroblin (β2-MG) excretion levels above 300 μg/g creatinine are used to indicate defective tubular reabsorption. Arguably, increased urinary β2-MG excretion could also reflect glomerular filtration rate decline. Thus, we investigated an association between urinary β2-MG and estimated glomerular filtration rate (eGFR). We studied 527 subjects, aged 30-87 years (mean 51.2), who lived in a rural area of Thailand polluted with cadmium (Cd). Of this cohort, 10.3% had urinary Cd levels <2 μg/g creatinine and 53.5% had urinary Cd levels ≥5 μg/g creatinine. Half (53.1%) of the participants had urinary β2-MG levels ≥ 300 μg/g creatinine, and 11.6% had low GFR, defined as eGFR <60 mL/min/1.73 m². Lower eGFR values were associated with older age (β = -0.568, P < 0.001), higher urinary β2-MG (β = -0.170, P < 0.001), higher urinary Cd (β = -0.103, P = 0.005) and diabetes (β = 0.074, P = 0.032). An inverse association between eGFR and urinary β2-MG was evident in subjects with low GFR (β = -0.332, P = 0.033), but not in those with GFR >90 mL/min/1.73 m² (β = -0.008, P = 0.896). These findings suggested Cd-induced nephron loss and reduced tubular reabsorption in low eGFR subjects. Urinary β2-MG levels <300 μg/g creatinine were associated with 4.66 (95% CI: 1.92, 11.32) fold increase in the POR for low GFR, compared with urinary β2-MG levels <100 μg/g creatinine. Findings in the present study cast doubt on a cut-off value for urinary β2-MG, while lending support to the notion that elevated urinary β2-MG excretion could indicate a fall of GFR.

Differences in Kidney Function Estimates Based on Creatinine and/or Cystatin C in Non-Traumatic Amputation Patients and Their Impact on Drug Prescribing

Accurate kidney function estimates are necessary when prescribing renally-eliminated medications. Our objectives were to investigate how amputation affects estimated glomerular filtration rate (eGFR) and to determine if dosing recommendations differ among different eGFR equations. In a cohort study of non-traumatic amputation patients, eGFR based on creatinine and/or cystatin C were measured before and after amputation. Prescribed, renally-eliminated medications were compared with dosing guidelines in Renbase^®. Data from 38 patients with a median age of 75 years were analyzed. The median (range) eGFR was 65 (15⁻103), 38 (13⁻79), and 48 (13⁻86) mL/min/1.73 m² before amputation and 80 (22⁻107), 51 (13⁻95), and 62 (16⁻100) mL/min/1.73 m² after amputation for eGFR_Creatinine, eGFR_CystatinC, and eGFR_Combined, respectively (p < 0.01). From before to after amputation, eGFR increased on average by 8.5, 6.1, and 7.4 mL/min/1.73 m² for eGFR_Creatinine, eGFR_CystatinC, and eGFR_Combined (all p < 0.01), respectively. At least one renally-eliminated medication was prescribed at a higher dose than recommended in 37.8% of patients using eGFR_CystatinC, 17.6% using eGFR_Combined and 10.8% using eGFR_Creatinine. In conclusion, amputation affects eGFR regardless of the eGFR equations. The differences among equations would impact prescribing of renally-eliminated medications, particularly when switching from creatinine to cystatin C.

Comparison of the new and traditional CKD-EPI GFR estimation equations with urinary inulin clearance: A study of equation performance

BACKGROUND

Diagnosis, prognostication and treatment in chronic kidney disease is often informed by an estimate of the glomerular filtration rate (GFR). Commonly used GFR estimation (eGFR) equations are based on serum creatinine (Cr) concentrations and display suboptimal precision and accuracy. Newer equations incorporating additional endogenous markers such as β-Trace Protein (BTP), β₂-Microglobulin (B2M) and cystatin C (cysC) have been developed but require validation.

METHODS

This prospective cohort study evaluated the performance of 6 eGFR equations developed by the chronic kidney disease - epidemiology collaboration group (CKD-EPI) against urinary inulin clearance GFR in patients recruited from outpatient nephrology clinics.

RESULTS

Mean biases were negligible and similar between equations. The eGFR-EPI Cr/cysC had the best precision and accuracy of all the equations and the best agreement with inulin mGFR when classifying participants into GFR categories. The BTP and B2M equations displayed the worst precisions and accuracies and showed the least consistent performance across levels of GFR. Thus, the eGFR-EPI Cr/cysC is the least biased, most precise and has the highest accuracy as compared to other eGFR-EPI equations.

CONCLUSIONS

The BTP and B2M equations are the worst performing of the eGFR-EPI equations, and no benefit is observed with the addition of BTP or B2M to Cr/cysC.