Performance of cystatin C- and creatinine-based estimated glomerular filtration rate equations depends on patient characteristics

Estimation of renal function using iodine maps in dual-energy spectral computed tomography urography: a feasibility and accuracy study

PURPOSE

To explore the feasibility of measuring glomerular filtration rate (GFR) using iodine maps in dual-energy spectral computed tomography urography (DEsCTU) and correlate them with the estimated GFR (eGFR) based on the equation of creatinine-cystatin C.

MATERIALS AND METHODS

One hundred and twenty-eight patients referred for DEsCTU were retrospectively enrolled. The DEsCTU protocol included non-contrast, nephrographic, and excretory phase imaging. The CT-derived GFR was calculated using the above 3-phase iodine maps (CT-GFRiodine) and 120 kVp-like images (CT-GFR120kvp) separately. CT-GFRiodine and CT-GFR120kvp were compared with eGFR using paired t-test, correlation analysis, and Bland-Altman plots. The receiver operating characteristic curves were used to test the renal function diagnostic performance with CT-GFR120kvp and CT-GFRiodine.

RESULTS

The difference between eGFR (89.91 ± 18.45 ml·min-1·1.73 m-2) as reference standard and CT-GFRiodine (90.06 ± 20.89 ml·min-1·1.73 m-2) was not statistically significant, showing excellent correlation (r = 0.88, P < 0.001) and agreement (± 19.75 ml·min-1·1.73 m-2, P = 0.866). The correlation between eGFR and CT-GFR120kvp (66.13 ± 19.18 ml·min-1·1.73 m-2) was poor (r = 0.36, P < 0.001), and the agreement was poor (± 40.65 ml·min-1·1.73 m-2, P < 0.001). There were 62 patients with normal renal function and 66 patients with decreased renal function based on eGFR. The CT-GFRiodine had the largest area under the curve (AUC) for distinguishing between normal and decreased renal function (AUC = 0.951).

CONCLUSION

The GFR can be calculated accurately using iodine maps in DEsCTU. DEsCTU could be a non-invasive and reliable one-stop-shop imaging technique for evaluating both the urinary tract morphology and renal function.

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.

Impaired Renal Function and Major Cardiovascular Events in Young Adults

BACKGROUND

Cardiovascular (CV) disease in young adults (aged 18-39 years) is on the rise. Whether subclinical reductions in kidney function (ie, estimated glomerular filtration rate [eGFR] above the current threshold for chronic kidney disease but below age-expected values) are associated with elevated CV risk is unknown.

OBJECTIVES

The goal of this study was to examine age-specific associations of subclinical eGFR reductions in young adults with major adverse cardiovascular events (MACEs) and MACE plus heart failure (MACE+).

METHODS

A retrospective cohort study of 8.7 million individuals (3.6 million aged 18-39 years) was constructed using linked provincial health care data sets from Ontario, Canada (January 2008-March 2021). Cox models were used to examine the association of categorized eGFR (50-120 mL/min/1.73 m2) with MACE (first of CV mortality, acute coronary syndrome, and ischemic stroke) and MACE+, stratified according to age (18-39, 40-49, and 50-65 years).

RESULTS

In the study cohort (mean age 41.3 years; mean eGFR 104.2 mL/min/1.73 m2; median follow-up 9.2 years), a stepwise increase in the relative risk of MACE and MACE+ was observed as early as eGFR <80 mL/min/1.73 m2 in young adults (eg, for MACE, at eGFR 70-79 mL/min/1.73 m2, ages 18-30 years: 2.37 events per 1,000 person years [HR: 1.31; 95% CI: 1.27-1.40]; ages 40-49 years: 6.26 events per 1,000 person years [HR: 1.09; 95% CI: 1.06-1.12]; ages 50-65 years: 14.9 events per 1,000 person years [HR: 1.07; 95% CI: 1.05-1.08]). Results persisted for each MACE component and in additional analyses (stratifying according to past CV disease, accounting for albuminuria at index, and using repeated eGFR measures).

CONCLUSIONS

In young adults, eGFR below age-expected values were associated with an elevated risk for MACE and MACE+, warranting age-appropriate risk stratification, proactive monitoring, and timely intervention.

Lithium Therapy in Old Age: Recommendations from a Delphi Survey

INTRODUCTION

While lithium (Li) has been well established for the treatment of bipolar disorder, geriatric patients require special attention when it comes to issues of drug safety. Declining renal function, amongst other medical conditions, and polypharmacy may pose increased risks. Only a few previous studies have addressed the management of Li in geriatric patients.

METHODS

Twenty-four German medical experts on geriatric medicine and Li treatment participated in a Delphi survey, consisting of two rounds of questionnaires and a final formulation of treatment recommendations. Three major issues of Li therapy were outlined: initiation of treatment, monitoring of ongoing therapy, and withdrawal due to medical reasons. Final recommendations were consented to at a threshold of at least 80% expert agreement.

RESULTS

Final consensus was achieved on 21 clinical recommendations. The approved recommendations covered aspects of necessary laboratory checks, concomitant medication, and target Li serum concentration in geriatric patients. Concerning the termination of Li therapy, an agreement was reached on the appropriate time span for tapering and on potential alternatives to Li. No consensus was achieved on whether concomitant dementia or frailty should be considered contraindications for Li treatment and the appropriate threshold of the estimated glomerular function rate for withdrawing Li.

CONCLUSION

According to the view of German experts, Li may be used in geriatric patients, but it should be monitored carefully. However, the lack of consent in several specific treatment situations underlines the need for research on specific issues of Li therapy.

GFR estimated with creatinine rather than cystatin C is more reflective of the true risk of adverse outcomes with low GFR in kidney transplant recipients

BACKGROUND

Serum cystatin C-based estimated glomerular filtration rate (eGFRcys) generally associates with clinical outcomes better than serum creatinine-based eGFR (eGFRcr) despite similar precision in estimating measured GFR (mGFR). We sought to determine whether the risk of adverse outcomes with eGFRcr or eGFRcys was via GFR alone or also via non-GFR determinants among kidney transplant recipients.

METHODS

Consecutive adult kidney transplant recipients underwent a standardized GFR assessment during a routine follow-up clinic visit between 2011 and 2013. Patients were followed for graft failure or the composite outcome of cardiovascular (CV) events or mortality through 2020. The risk of these events by baseline mGFR, eGFRcr and eGFRcys was assessed unadjusted, adjusted for mGFR and adjusted for CV risk factors.

RESULTS

There were 1135 recipients with a mean baseline mGFR of 55.6, eGFRcr of 54.8 and eGFRcys of 46.8 ml/min/1.73 m2 and a median follow-up of 6 years. Each 10 ml/min/1.73 m2 decrease in mGFR, eGFRcr or eGFRcys associated with graft failure [hazard ratio (HR) 1.79, 1.68 and 2.07, respectively; P < .001 for all) and CV events or mortality outcome (HR 1.28, 1.19 and 1.43, respectively; P < .001 for all). After adjusting for mGFR, eGFRcys associated with graft failure (HR 1.57, P < .001) and CV events or mortality (HR 1.49, P < .001), but eGFRcr did not associate with either. After further adjusting for CV risk factors, risk of these outcomes with lower eGFRcys was attenuated.

CONCLUSION

eGFRcr better represents the true relationship between GFR and outcomes after kidney transplantation because it has less non-GFR residual association. Cystatin C is better interpreted as a nonspecific prognostic biomarker than is eGFR in the kidney transplant setting.

Associations between modest reductions in kidney function and adverse outcomes in young adults: retrospective, population based cohort study

OBJECTIVE

To study age specific associations of modest reductions in estimated glomerular filtration rate (eGFR) with adverse outcomes.

DESIGN

Retrospective, population based cohort study.

SETTING

Linked healthcare administrative datasets in Ontario, Canada.

PARTICIPANTS

Adult residents (18-65 years) with at least one outpatient eGFR value (categorized in 10 unit increments from 50 mL/min/1.73m2 to >120 mL/min/1.73m2), with no history of kidney disease.

MAIN OUTCOME MEASURES

eGFRs and hazard ratios of composite adverse outcome (all cause mortality, any cardiovascular event, and kidney failure) stratified by age (18-39 years, 40-49 years, and 50-65 years), and relative to age specific eGFR referents (100-110 mL/min/1.73m2) for ages 18-39 years, 90-100 for 40-49 years, 80-90 for 50-65 years).

RESULTS

From 1 January 2008 to 31 March 2021, among 8 703 871 adults (mean age 41.3 (standard deviation 13.6) years; mean index eGFR 104.2 mL/min/1.73m2 (standard deviation 16.1); median follow-up 9.2 years (interquartile range 5.7-11.4)), modestly reduced eGFR measurements specific to age were recorded in 18.0% of those aged 18-39, 18.8% in those aged 40-49, and 17.0% in those aged 50-65. In comparison with age specific referents, adverse outcomes were consistently higher by hazard ratio and incidence for ages 18-39 compared with older groups across all eGFR categories. For modest reductions (eGFR 70-80 mL/min/1.73m2), the hazard ratio for ages 18-39 years was 1.42 (95% confidence interval 1.35 to 1.49), 4.39 per 1000 person years; for ages 40-49 years was 1.13 (1.10 to 1.16), 9.61 per 1000 person years; and for ages 50-65 years was 1.08 (1.07 to 1.09), 23.4 per 1000 person years. Results persisted for each individual outcome and in many sensitivity analyses.

CONCLUSIONS

Modest eGFR reductions were consistently associated with higher rates of adverse outcomes. Higher relative hazards were most prominent and occurred as early as eGFR <80 mL/min/1.73m2 in younger adults, compared with older groups. These findings suggest a role for more frequent monitoring of kidney function in younger adults to identify individuals at risk to prevent chronic kidney disease and its complications.

Impact of New eGFR Equations on Risk Assessment In Patients Undergoing Transcatheter Aortic Valve Implantation

BACKGROUND

Recently, the Chronic Kidney Disease-Epidemiology Collaboration working group has published new formulas for race-independent estimation of glomerular filtration rate (GFR). We investigated the old and new eGFR equations in patients transcatheter aortic valve implantation (TAVI).

METHODS

We conducted a retrospective analysis based on the data from a prospective registry of patients who underwent TAVI from January 2008 to May 2019. The primary endpoint was 30-day mortality after TAVI, and the secondary endpoints included one- and three-year mortality.

RESULTS

In total, 1792 patients undergoing TAVI were included in the present analysis. The thirty-day mortality was 4.6 % (95 % CI 3.8-5.7 %), and the one- and three-year mortality were 17.5 % (95 % CI 15.7-19.4 %) and 34.4 % (95 % CI 32.0-37.0 %). After the application of the new eGFR formula, 12.0 % of patients were reclassified within the GFR category in CKD, while 13.2 % of patients were reclassified within the GFR categories of the EuroSCORE II. Hazard ratios for 30-day, one-year, and three-year mortality increased after introduction of the new creatine-based eq. (1.51, 1.52, 1.49 vs. 1.87, 1.79, 1.74, respectively). Compared to the old equation, the new eGFR <60 ml/min/1.73 m² had a better discrimination ability for the 30-day mortality (Harell's C: 0.563 (95 % CI 0.518-0.608) vs, 0.583 (95 % CI 0.546-0.636); delta Harell's C, 0.031 ± 0.022, p < 0.001). Similar findings were consistently observed in the cystatin creatinine-based equations.

CONCLUSIONS

The application of the new race-independent estimators of GFR results in the reassessment of renal function in a significant proportion of TAVI patients and may influence the risk stratification of this population.

Comparison of the 2021 and 2009 Chronic Kidney Disease Epidemiology Collaboration Creatinine equation for estimated glomerular filtration rate in a Chinese population

OBJECTIVES

To retrospectively compare the clinical effects of the newly released 2021 and 2009 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations for estimated glomerular filtration rate based on creatinine (eGFRcr) in a Chinese population with a broad spectrum of clinical characteristics using historical data.

DESIGN AND METHODS

Patients and healthy individuals who visited the Zhongshan Hospital, Fudan University, between July 1, 2020, and July 1, 2022, were enrolled. The exclusion criteria were age < 18 years, amputees, pregnant women, patients with muscle-related diseases, and patients who had undergone ultrafiltration or dialysis. The final study population included 1,051,827 patients with a median age of 57 years; 57.24% of the enrolled individuals were men. eGFRcr was calculated using the 2009 and 2021 CKD-EPI equations and initial creatinine level. Results were evaluated statistically by sex, age, creatinine level, and CKD stage.

RESULTS

The 2021 equation increased the eGFRcr in all participants compared to the 2009 equation by 4.46%. The median eGFRcr deviation of the 2021 CKD-EPI equation compared to the 2009 CKD-EPI equation was 4 ml/min/1.73 m². 903443 subjects (85.89%) had higher eGFRcr owing to the utilization of the 2021 CKD-EPI equation, which did not cause CKD stage change. A total of 11.57% of subjects (121,666) had improved CKD stage with the 2021 CKD-EPI equation. 1.79% (18,817) had the same CKD stage with both equations, and 0.75% (7,901) had lower eGFRcr but no change in the CKD stage with the 2021 equation.

CONCLUSIONS

The 2021 CKD-EPI equation typically produces higher eGFRcr results than the 2009 version. Applying the new equation could lead to changes in the CKD stage for some patients, which doctors should consider. .

Investigations of Renal Function and Age-Related Macular Degeneration Phenotypes

PURPOSE

To investigate potential associations between renal function and age-related macular degeneration (AMD) features as assessed with multimodal retinal imaging.

METHODS

A subset of participants included in a dark adaptation study with varying AMD severities had estimated glomerular filtration rate (eGFR) values (mL/min/1.73 m2) obtained from renal function laboratory testing of serum creatinine and cystatin C. Multimodal imaging from visit dates associated with serum samples was graded by the Wisconsin Reading Center for AMD features. Associations of eGFR with AMD features and severity grades, age, smoker status and rod-intercept time were investigated. Simple univariate analyses, age-corrected multivariate analyses, and a feature-selecting least absolute shrinkage and selection operator regression were performed for eGFR as a continuous dependent variable.

RESULTS

A total of 110 patients (mean age, 75.1 ± 9.4 years; mean eGFR, 70.7 ± 18.2 mL/min/1.73 m2) were included. In univariate analyses age (estimate, -1.16 units/year; 95% confidence interval [CI], -1.46 to -0.87; P < 0.0001), rod-intercept time (estimate, -0.54 units/minute; 95% CI, -0.81 to -0.27; P < 0.001) and subretinal drusenoid deposits (-11.12 units for subretinal drusenoid deposit presence in either eye; 95% CI, -20.23 to -2.01; P = 0.017) were associated with decreased renal function. However, in age-corrected multivariate models, age was the only significant variable associated with renal function, confirmed by least absolute shrinkage and selection operator regression.

CONCLUSIONS

Accounting for age, renal function parameters did not show an association with AMD features.

TRANSLATIONAL RELEVANCE

Bruch's membrane of the eye and the glomerular basement membrane of the kidney share physiologic similarities such that decreased renal function may demonstrate associations with AMD phenotypes.

Serum myo-inositol and valine improve metabolomic-based estimated glomerular filtration rate among kidney transplant recipients

BACKGROUND

Close monitoring of glomerular filtration rate (GFR) is essential for the management of patients post kidney transplantation. Measured GFR (mGFR), the gold standard, is not readily accessible in most centers. Furthermore, the performance of new estimated GFR (eGFR) equations based upon creatinine and/or cystatin C have not been validated in kidney transplant patients. Here we evaluate a recently published eGFR equation using cystatin C, creatinine, myo-inositol and valine as measured by nuclear magnetic resonance (eGFRNMR).

METHODS

Residual sera was obtained from a cohort of patients with clinically ordered iothalamate renal clearance mGFR (n = 602). Kidney transplant recipients accounted for 220 (37%) of participants.

RESULTS

Compared to mGFR, there was no significant bias for eGFRcr or eGFRNMR, while eGFRcr-cys significantly underestimated mGFR. P30 values were similar for all eGFR. P15 was significantly higher for eGFRNMR compared to eGFRcr, while the P15 for eGFRcr-cys only improved among patients without a kidney transplant. Agreement with mGFR CKD stages of <15, 30, 45, 60, and 90 ml/min/1.73 m2 was identical for eGFRcr and eGFRcr-cys (61.8%, both cases) while eGFRNMR was significantly higher (66.4%) among patients with a kidney transplant.

CONCLUSION

The 2021 CKD-EPI eGFRcr and eGFRcr-cys have similar bias, P15, and agreement while eGFRNMR more closely matched mGFR with the strongest improvement among kidney transplant recipients.

Change of renal function after short-term use of cardioprotective agents in patients with type 2 diabetes is not accurately assessed by the change of estimated glomerular filtration rate: an observational study

BACKGROUND

After initiating cardioprotective agents, a fall of estimated glomerular filtration rate (eGFR) has been reported in several studies. Our goal was to evaluate the accuracy of change of Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) eGFR in patients with type 2 diabetes (T2D) after short-term pharmacological intervention with angiotensin-converting enzyme inhibitor, angiotensin-receptor blocker, gliptin or sodium-glucose cotransporter-2 inhibitor.

METHODS

We analyzed 190 patients with T2D in the early stage of the disease, having no overt renal impairment by CKD-EPI equation. In each patient, we measured GFR (mGFR) by applying the constant infusion input clearance technique with sinistrin (Inutest; Fresenius, Linz, Austria) at baseline and after short-term (4-12 weeks) pharmacological intervention with cardioprotective agents (ramipril, telmisartan, linagliptin, metformin, empagliflozin) that potentially lead to an alteration of renal function. Simultaneously, a standardized analysis of serum creatinine was performed and eGFR was estimated by the CKD-EPI equation.

RESULTS

Average mGFR was 111 ± 20 ml/min/1.73m², whereas eGFR was lower with 93 ± 13 ml/min/1.73m². The ratio eGFR/mGFR in relation to mGFR was almost curvilinear, showing an underestimation of renal function by eGFR in the upper normal range. At baseline only 80 patients (42%) lay within ± 10% of mGFR and the concordance correlation coefficient (CCC) was extremely low (- 0.07). After short-term pharmacological intervention changes in eGFR and mGFR correlated with each other (r = 0.286, p < 0.001). For example, for a given mGFR of 111 ml/min/1.73m², a change of mGFR by ± 10% corresponded to ± 11 ml/min/1.73m², but the confidence interval of eGFR was 25 ml/min/1.73m². The CCC was low (0.22).

CONCLUSION

The agreement between eGFR by CKD-EPI and mGFR is modest and the change of renal function after short-term pharmacological intervention is not accurately and precisely reflected by the change of eGFR in patients with T2D in the early stage of their disease.

Assessing Renal Function for Kidney Donation. How Low Is Too Low?

Kidney transplantation (KT) is the treatment of choice for patients with end-stage kidney disease (ESKD) with decreased morbi-mortality, improved life quality, and reduced cost. However, the shortage of organs from deceased donors led to an increase in KT from living donors. Some stipulate that living donors have a higher risk of ESKD after donation compared with healthy non-donors. The reason for this is not clear. It is possible that ESKD is due to the nephrectomy-related reduction in glomerular filtration rate (GFR), followed by an age-related decline that may be more rapid in related donors. It is essential to assess donors properly to avoid rejecting suitable ones and not accepting those with a higher risk of ESKD. GFR is a central aspect of the evaluation of potential donors since there is an association between low GFR and ESKD. The methods for assessing GFR are in continuous debate, and the kidney function thresholds for accepting a donor may vary according to the guidelines. While direct measurements of GFR (mGFR) provide the most accurate evaluation of kidney function, guidelines do not systematically use this measurement as a reference. Also, some studies have shown that the GFR decreases with age and may vary with gender and race, therefore, the lower limit of GFR in patients eligible to donate may vary based on these demographic factors. Finally, it is known that CrCl overestimates mGFR while eGFR underestimates it, therefore, another way to have a reliable GFR could be the combination of two measurement methods.

A Deep Learning Approach for the Estimation of Glomerular Filtration Rate

An accurate estimation of glomerular filtration rate (GFR) is clinically crucial for kidney disease diagnosis and predicting the prognosis of chronic kidney disease (CKD). Machine learning methodologies such as deep neural networks provide a potential avenue for increasing accuracy in GFR estimation. We developed a novel deep learning architecture, a deep and shallow neural network, to estimate GFR (dlGFR for short) and examined its comparative performance with estimated GFR from Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. The dlGFR model jointly trains a shallow learning model and a deep neural network to enable both linear transformation from input features to a log GFR target, and non-linear feature embedding for stage of kidney function classification. We validate the proposed methods on the data from multiple studies obtained from the NIDDK Central Database Repository. The deep learning model predicted values of GFR within 30% of measured GFR with 88.3% accuracy, compared to the 87.1% and 84.7% of the accuracy achieved by CKD-EPI and MDRD equations (p=0.051 and p<0.001, respectively). Our results suggest that deep learning methods are superior to equations resulting from traditional statistical methods in estimating glomerular filtration rate. Based on these results, an end-to-end predication system has been deployed to facilitate use of the proposed dlGFR algorithm.

National Kidney Foundation Laboratory Engagement Working Group Recommendations for Implementing the CKD-EPI 2021 Race-Free Equations for Estimated Glomerular Filtration Rate: Practical Guidance for Clinical Laboratories

Recognizing that race is a social and not a biological construct, healthcare professionals and the public have called for removal of race in clinical algorithms. In response, the National Kidney Foundation and the American Society of Nephrology created the Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases to examine the issue and provide recommendations. The final report from the Task Force recommends calculating estimated glomerular filtration rate (eGFR) without a race coefficient using the recently published CKD-EPI 2021 creatinine and creatinine-cystatin C equations. The Task Force recommends immediately replacing older eGFRcr equations (MDRD Study and CKD-EPI 2009) with the new CKD-EPI 2021 equation. In a 2019 survey by the College of American Pathologists, 23% of 6200 laboratories reporting eGFRcr used an incorrect equation that is not suitable for use with standardized creatinine measurements, 34% used the CKD-EPI 2009 equation and 43% used the MDRD Study 2006 equation re-expressed for standardized creatinine measurement. Rapid transition to using the CKD-EPI 2021 equation is an opportunity for laboratories to standardize to a single equation to eliminate differences in eGFRcr due to different equations used by different laboratories, and to report eGFR without use of race. We provide guidance to laboratories for implementing the CKD-EPI 2021 equations for both eGFRcr and eGFRcr-cys.

Biomarker-Guided Risk Assessment for Acute Kidney Injury: Time for Clinical Implementation?

Acute kidney injury (AKI) is a common and serious complication in hospitalized patients, which continues to pose a clinical challenge for treating physicians. The most recent Kidney Disease Improving Global Outcomes practice guidelines for AKI have restated the importance of earliest possible detection of AKI and adjusting treatment accordingly. Since the emergence of initial studies examining the use of neutrophil gelatinase-associated lipocalin (NGAL) and cycle arrest biomarkers, tissue inhibitor metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein (IGFBP7), for early diagnosis of AKI, a vast number of studies have investigated the accuracy and additional clinical benefits of these biomarkers. As proposed by the Acute Dialysis Quality Initiative, new AKI diagnostic criteria should equally utilize glomerular function and tubular injury markers for AKI diagnosis. In addition to refining our capabilities in kidney risk prediction with kidney injury biomarkers, structural disorder phenotypes referred to as "preclinical-" and "subclinical AKI" have been described and are increasingly recognized. Additionally, positive biomarker test findings were found to provide prognostic information regardless of an acute decline in renal function (positive serum creatinine criteria). We summarize and discuss the recent findings focusing on two of the most promising and clinically available kidney injury biomarkers, NGAL and cell cycle arrest markers, in the context of AKI phenotypes. Finally, we draw conclusions regarding the clinical implications for kidney risk prediction.

Renal-Cerebral Pathophysiology: The Interplay Between Chronic Kidney Disease and Cerebrovascular Disease

OBJECTIVES

Cerebrovascular disease has increasingly been linked to overall vascular health. Pathologic conditions like diabetes, hypertension, and kidney disease have been shown to affect brain health and cerebrovascular and nervous systems. Acute kidney injury (AKI) and chronic Kidney Disease (CKD) represent a variety of vascular insults that can adversely affect cerebral health. Hypertension, fluctuations in blood pressure, and diabetic vasculopathy are known risk factors for cerebrovascular disease associated with CKD. Other emerging areas of interest include endothelial dysfunction, vascular calcification due to calcium and phosphorus metabolism dysregulation, and uremic neuropathy present the next frontier of investigation in CKD and cerebrovascular health.

METHODS

It has become apparent that the interrelation of AKI and CKD with vascular health, chemical homeostasis, and hormonal regulation upset many aspects of cerebral health and functioning. Stroke is an obvious connection, with CKD patients demonstrating a higher proclivity for cerebrovascular accidents. Cerebral bleeding risk, uremic neuropathies, sodium dysregulation with impacts on nervous system, vascular calcification, and endothelial dysfunction are the next salient areas of research that are likely to reveal key breakthroughs in renal-cerebral pathophysiology.

RESULTS

In this review nephrological definition are discussed in a neuro-centric manner, and the areas of key overlap between CKD and cerebrovascular pathology are discussed. The multifaceted effects of renal function on the health of the brain are also examined.

CONCLUSION

This review article aims to create the background for ongoing and future neurological-nephrological collaboration on understanding the special challenges in caring for patients with cerebrovascular disease who also have CKD.

Comparison of bias and accuracy using cystatin C and creatinine in CKD-EPI equations for GFR estimation

BACKGROUND

The directly measured glomerular filtrate rate (mGFR) is the gold standard for kidney function, but it is invasive and costly. The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations have been widely used to estimate GFR, however, the comparative accuracy of estimated GFR (eGFR) using creatinine and cystatin C in CKD-EPI equations remains unclear. We performed this meta-analysis to assess the bias and accuracy of eGFR using equations of CKD-EPI_crea, CKD-EPI_cys, and CKD-EPI_crea/cys in adult populations relevant to primary health care.

METHODS

Pubmed, Web of Science, EMBASE, and the Cochrane Library were searched from inception until December 2019 for related studies.

RESULTS

A total of 35 studies with 23,667 participants, which reported the data on the bias, and/or P30, and/or R were included. The difference in the bias of eGFR using CKD-EPI_cys was 4.84 mL/min/1.73 m² (95% CI, 1.88~7.80) lower than using CKD-EPI_crea, and 1.50 mL/min/1.73 m² (95% CI, 0.05~2.95) lower than using CKD-EPI_crea/cys. These gaps increased in subgroups of low mGFR (<60 mL/min/1.73 m²). CKD-EPI_crea/cys eGFR achieved the highest accuracy, 7.50% higher than CKD-EPI_crea (95% CI, 4.81~10.18), and 3.21% higher than CKD-EPI_cys (95% CI, -0.43~6.85); and the best correlation with mGFR, with Fisher's z transformed R of 1.20 (95% CI, 0.89-1.50).

CONCLUSIONS

CKD-EPI_crea/cys and CKD-EPI_cys gave less bias and more accurate estimates of mGFR than CKD-EPI_crea. More variables and coefficients could be added in CKD-EPI equations to achieve less bias and more accuracy in future research.

Population Pharmacokinetic Study of Ceftriaxone in Elderly Patients, Using Cystatin C-Based Estimates of Renal Function To Account for Frailty

Ceftriaxone is widely used for respiratory and urinary infections in elderly and frail patients, but there are few pharmacokinetic studies. A prospective population pharmacokinetic study of ceftriaxone in adults over 65 years old was undertaken. Dried blood spots collected at baseline (predose) and 0.5, 1, 4, 8, and 24 h after administration of 1 g of ceftriaxone were assayed using a validated liquid chromatography-mass spectroscopy analytical method. Frailty was classified using the Edmonton frailty scale and grip strength via a hand dynamometer. Estimates of glomerular filtration rate were determined using creatinine-based and cystatin C-based equations. Of 26 patients recruited, 23 (88%) were vulnerable or very frail. Estimates of drug clearance improved significantly with a cystatin C-based estimate of renal function that accounted for frailty. Simulations indicate that the combined effects of ranges of size and renal function resulted in a 6-fold range in peak ceftriaxone concentrations and 9-fold range in total exposure (area under the concentration-time curve [AUC]). For elderly patients with moderate or severe renal impairment, 48-h dosing results in greater trough concentrations and total exposure than the trough concentrations and total exposure in patients with normal renal function receiving 24-h dosing. Cystatin C-based measures of renal function improved predictions of ceftriaxone clearance in elderly patients.

Patterns of Cystatin C Uptake and Use Across and Within Hospitals

OBJECTIVE

To characterize the use of cystatin C (cysC) across and within hospitals.

PATIENTS AND METHODS

This 2-part study first evaluated access to cysC testing across 129 hospitals in the state of Minnesota, using a telephone-based survey. Second, granular data from a single center (Mayo Clinic) with on-site, rapid-turnaround testing (<1 day) and automated estimated glomerular filtration rate (eGFR) reporting was used to describe temporal patterns. The characteristics of hospitals that offered cysC testing and of patients who underwent rapid cysC testing at Mayo Clinic between January 1, 2011, and March 31, 2018, were described. Poisson regression analyzed temporal trends in cysC testing.

RESULTS

Of the 114 hospitals (88%) that responded to the statewide survey, cysC was available in 91 (80%), but only 3 of 91 (3%) reported a turnaround time of <1 day. At Mayo Clinic, cysC use increased from 0.74 tests per 1000 patient-days in 2011 to 14 tests per 1000 patient-days in 2018 (P=.004). Of the 3774 patients with cysC tests, the mean first available eGFR was 46 mL/min per 1.73 m2 using cysC and 59 mL/min per 1.73 m2 using serum creatinine (P<.001). CysC testing was used across all intensities of care and was ordered by a variety of specialties. Nephrology was consulted in only 42% of cases.

CONCLUSION

In the hospital, rapid-turnaround cysC testing is necessary for practical use but was not widely available in Minnesota. When available, a marked increase in cysC testing was observed over the study timeframe. Additional research is needed to determine optimal strategies for implementation of cysC within hospitals.

Prevalence and Risk Factors of CKD in South Kivu, Democratic Republic of Congo: A Large-Scale Population Study

Background

The prevalence of chronic kidney disease (CKD) in African American individuals is high but whether this applies to native populations in sub-Saharan Africa is unclear.

Methods

In a cross-sectional study, we assessed the prevalence and risk factors of CKD in rural and urban adults in South Kivu, Democratic Republic of Congo. Glomerular filtration rate (GFR) was estimated using the CKD–Epidemiology Collaboration (CKD-EPI) equations based on serum creatinine (eGFRcr), cystatin C (eGFRcys), or both markers (eGFRcr-cys), without ethnic correction factor. CKD was defined as an eGFR <60 ml/min per 1.73 m² and/or albuminuria (albumin-to-creatinine ratio ≥30 mg/g).

Results

A total of 1317 participants aged 41.1 ± 17.1 years (730 rural, 587 urban) were enrolled. The prevalence of hypertension (20.2%; 95% confidence interval [CI], 18–22.3), diabetes mellitus (4.3%; 95% CI, 3.2–5.4) and obesity (8.9%; 95% CI, 7.4–10.5) was higher in urban than rural participants (all P < 0.05). HIV infection prevalence was 0.41% (95% CI, 0.05–0.78). The prevalence of eGFRcr <60 ml/min per 1.73 m² was 5.4% (95% CI, 4.2–6.7). The prevalence of albuminuria was 6.6% (95 % CI, 5.1–8.1). The overall prevalence of CKD was 12.2% (95% CI, 10.2–14.2) according to CKD-EPIcr. Factors independently associated with CKD-EPIcr were older age (adjusted odds ratio [aOR], 1.05 [1.04–1.07]), urban residence (aOR 1.86 [1.18–2.95]), female sex (aOR 1.66 [1.04–2.66]), hypertension (aOR 1.90 [1.15–3.12]), diabetes (aOR 2.03 [1.02–4.06]), and HIV infection (10.21 [2.75–37.85]). The results based on eGFRcys or eGFRcr-cys were largely consistent with the preceding.

Conclusion

Overall, the burden of CKD is substantial (>11%), predominantly in the urban area, and largely driven by classic risk factors (gender, aging, HIV, hypertension, and diabetes).

Predictors of Augmented Renal Clearance in a Heterogeneous ICU Population as Defined by Creatinine and Cystatin C

INTRODUCTION

The incidence of augmented renal clearance (ARC) in the intensive care unit (ICU) is highly variable, and identification of these patients remains challenging.

OBJECTIVE

The objective of this study was to define the incidence of ARC in a cohort of critically ill adults, using serum Cr and cystatin C, and to identify factors associated with its development.

METHODS

This is a retrospective cohort study of critically ill patients without stage 2 or 3 acute kidney injury with both serum Cr and cystatin C available. The incidence of ARC was defined as a Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)Cr-cystatin C-estimated glomerular filtration rate >130 mL/min. A multivariable logistic regression model using a penalized Lasso method was fit to identify independent predictors of ARC.

RESULTS

Among the 368 patients included in the study, indication for ICU admission was nonoperative in 55% of patients, and 9% of patients were admitted for major trauma. The overall incidence of ARC was low at 4.1%. In a multivariable logistic regression model, Charlson comorbidity index, major trauma, intracerebral hemorrhage, age, and Sequential Organ Failure Assessment score were found to predict ARC.

CONCLUSION

The incidence of ARC in this study was low, but prediction models identified several factors for early identification of patients with risk factors for or who develop ARC, particularly in a cohort with a low baseline risk of ARC. These factors could be used to help identify patients who may develop ARC.

Comparison of MDRD and the old CKD-EPI equations with the new CKD-EPI equations in kidney transplant patients when glomerular filtration rate is measured with 51Cr-EDTA

BACKGROUND

When estimating the glomerular filtration rate (GFR) in kidney transplant patients, significant differences have been found between MDRD and the 2009 CKD-EPI equations, and reference techniques.

OBJECTIVE

To analyse and compare the performance of MDRD and the 2009 and 2012 CKD-EPI equations against ⁵¹Cr-EDTA plasma clearance in measuring GFR in 270 kidney transplant patients after one year.

RESULTS

The mean measured GFR was 43.0±11.4 (18.2-79.4)ml/min/1.73m², with creatinine levels of 1.42±0.46 (0.60-4.33)mg/dl and cystatin C levels of 1.45±0.53 (0.42-3.48)mg/l. This correlated moderately with creatinine (r=-0.61, P<.001) and cystatin C (r=-0.52, P<.001). Using linear regression techniques, it was found that creatinine, cystatin C, gender and age only explained 52% of GFR total variance. All equations overestimated GFR, with a mean bias of +11.1ml/min/1.73m² for MDRD, +16.4ml/min/1.73m² for 2009-CKD-EPI, +15ml/min/1.73m² for CKD-EPI with cystatin C, and +14.1ml/min/1.73m² for 2012-CKD-EPI with creatinine and cystatin C. eGFR by MDRD and the 2009 CKD-EPI equation correlated better with ⁵¹Cr-EDTA than CKD-EPI with creatinine and/or cystatin C. The overestimations were negatively correlated with creatinine and cystatin C levels, most significantly for CKD-EPI with creatinine and/or cystatin C when GFR was greater than 60ml/min/1.73m².

CONCLUSIONS

The 2012 CKD-EPI equations with creatinine and/or cystatin C significantly overestimate GFR in stage 1 and 2 chronic kidney disease. The MDRD equations is therefore recommended in these cases. The reference method used to measure GFR seems to heavily influence the bias of the equations.

Evaluation of cystatin C-derived glomerular filtration rate equations in Chinese population

ABTRACTGlomerular filtration rate (GFR) has become the best indicator for assessing renal function. This study aims to validate the existing cystatin C (CysC)-derived estimated glomerular filtration rate (eGFR) equations in Chinese patients to explore whether the reported CysC-derived eGFR formulas could be applied to the Chinese population. This study validated the equations in a population totaling 1816 inpatients. We calculated eGFR by different CysC-derived equations, then compared with the mGFR. Equation performance was assessed by bias (mean difference between mGFR and eGFR), precision (inter-quartile range of difference) and accuracy (mainly, accuracy within 30% [P₃₀]). All equations expressed poor performance in dialysis patients (n = 345), and the performance for non-dialysis patients (n = 1471) were significantly greater than that in dialysis patients. Feng and Pei equations had higher P₃₀ (50.82% and 49.73%, respectively) than the widely used CKD-EPI_CysC (41.10%) and MacIsaac equations (48.23%), and the distribution of eGFR values is more similar to the distribution of mGFR in non-dialysis patients. Similar trends showed in mGFR, sex, age, and BMI subgroups. However, no equation met the guideline standard of P₃₀ ≥ 75%. Our results suggest that the published CysC-based eGFR equations are not suitable for dialysis patients, and the accuracy of equations for non-dialysis patients significantly better than the dialysis ones. Moreover, Feng and Pei equation showed better performance in non-dialysis patients.

Impact of Long-Term Lithium Treatment on Renal Function in Patients With Bipolar Disorder Based on Novel Biomarkers

BACKGROUND

Lithium in the form of lithium carbonate (Li2CO3) has become one of the most effective and widely prescribed drugs for mood stabilization. However, lithium has adverse effects on renal tubular functions, such as decreased concentrating function of the kidneys, and even occasional symptoms of nephrogenous diabetes insipidus occur with additional evidence of glomerular disruption in lithium-treated patients.

METHODS

We assessed the kidney function of patients with bipolar disorder who are under long-term lithium treatment using novel markers of kidney damage such as plasma neutrophil gelatinase-associated lipocalin, cystatin C, albuminuria, estimated glomerular filtration rate, Chronic Kidney Disease-Epidemiology Investigation using creatinine and cystatin C, and serum and urinary osmolality, and compared the results with those of age-matched patients with bipolar disorder not treated with lithium. The study enrolled 120 patients with bipolar disorder, consisting of 80 (30 male and 50 female patients) who have been receiving lithium for 0.5 to 20 (mean, 7) years and 40 (10 male and 30 female patients) who had never been exposed to lithium treatment.

RESULTS

Patients treated with lithium had significantly decreased urine osmolality (mean ± SD, 405 ± 164 vs 667 ± 174 mmol/kg) and urine-to-serum osmolality ratio (1.35 ± 0.61 vs 2.25 ± 0.96). No significant difference was found in creatinine, estimated glomerular filtration rate values calculated using the Chronic Kidney Disease-Epidemiology Investigation using creatinine and cystatin C, neutrophil gelatinase-associated lipocalin, cystatin C, and albuminuria between both groups. We found no significant difference in renal biomarkers between patients treated with lithium for 6 to 24 months and those treated for 25 to 240 months.

CONCLUSIONS

We found significantly decreased kidney concentrating ability in the long-term lithium-treated patients compared with the control group. Other renal function markers did not indicate any significant signs of renal dysfunction.

Creatinine- and cystatin C-based estimated glomerular filtration rate slopes for the prediction of kidney outcome: a comparative retrospective study

BACKGROUND

Many studies have evaluated the usefulness of creatinine- (eGFRcr) and cystatin C-based estimated glomerular filtration rate (eGFRcys) at specific time points in predicting renal outcome. This study compared the performance of both eGFR changing slopes in identifying patients at high risk of end-stage renal disease (ESRD).

METHODS

From 2012 to 2017, patients with more than three simultaneous measurements of serum creatinine and cystatin C for 1 year were identified. Rapid progression was defined as eGFR slope < - 5 mL/min/1.73 m²/year. The primary outcome was progression to ESRD.

RESULTS

Overall, 1323 patients were included. The baseline eGFRcr and eGFRcys were 39 (27-48) and 38 (27-50) mL/min/1.73 m², respectively. Over 2.9 years (range, 2.0-3.8 years) of follow-up, 134 subjects (10%) progressed to ESRD. Both the eGFRcr and eGFRcys slopes were associated with a higher risk of ESRD, independently of baseline eGFR (hazard ratio [HR] = 0.986 [0.982-0.991] and HR = 0.988 [0.983-0.993], respectively; all p <  0.001). The creatinine- and cystatin C-based rapid progressions were associated with increased risk of ESRD (HR = 2.22 [1.57-3.13], HR = 2.03 [1.44-2.86], respectively; all p <  0.001). In the subgroup analyses, the rapid progression group, defined on the basis of creatinine levels (n = 503), showed no association between the eGFRcys slope and ESRD risk (p = 0.31), whereas the eGFRcr slope contributed to further discriminating higher ESRD risk in the subjects with rapid progression based on eGFRcys slopes (n = 463; p = 0.003).

CONCLUSIONS

Both eGFR slopes were associated with future ESRD risk. The eGFRcr slope was comparable with the eGFRcys slope in predicting kidney outcome.

eGFR and coronary artery calcification in chronic kidney disease

BACKGROUND

The independent association between eGFR and coronary artery calcification (CAC) is complex and not clear. The aim of this study is to investigate the relationship between eGFR calculated from different equations and CAC in predialysis CKD patients in Korea.

METHODS

In this cross-sectional study, we analyzed 1,533 patients from the KNOW-CKD cohort. eGFR was calculated by a four-variable MDRD equation (eGFR_MDRD ), CKD-EPI creatinine equations (eGFR_{C r} ), CKD-EPI Cystatin C equation (eGFR_{C ys} ), and CKD-EPI Creatinine-Cystatin equation (eGFR_{C rC ys} ). Participants were divided into eGFR categories (< 30, 30-59, 60-89, ≥ 90 ml/min/1.73 m² ). CACS (coronary artery calcium score) was measured using cardiac computed tomography. CAC was defined as CACS > 100.

RESULTS

CAC was found in 334 (21.8%) patients, and was more prevalent in the lower eGFR groups (p < 0.001). In multivariate Tobit regression, CACS increased gradually as eGFR_{C rC ys} decreased (p for trend = 0.034). In multivariate logistic regression, there were gradual associations between lower eGFR and CAC when an eGFR_{C ys} or eGFR_{C rC ys} was used. The adjusted OR for CAC in the group with eGFR < 30 ml/min/1.73m² compared to the group with eGFR ≥ 90 ml/min/1.73m² was 2.64 (95% CI, 1.09-3.60) when eGFR_{C rC ys} was used. Of the four eGFR formulas, only adding eGFR_{C rC ys} significantly improved CAC prediction models without eGFR (p = 0.046).

CONCLUSIONS

There was a gradual and independent association between low eGFR and CAC in a predialysis CKD cohort in Korea. eGFR_{C rC ys} predicted CAC better than other equations in this population. This article is protected by copyright. All rights reserved.

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.

Comparison of equations for estimating glomerular filtration rate in screening for chronic kidney disease in asymptomatic black Africans: a cross sectional study

BACKGROUND

Several equations have been developed to estimate glomerular filtration rate (eGFR). The common equations used were derived from populations predominantly comprised of Caucasians with chronic kidney disease (CKD). Some of the equations provide a correction factor for African-Americans due to their relatively increased muscle mass and this has been extrapolated to black Africans. Studies carried out in Africa in patients with CKD suggest that using this correction factor for the black African race may not be appropriate. However, these studies were not carried out in healthy individuals and as such the extrapolation of the findings to an asymptomatic black African population is questionable. We sought to compare the proportion of asymptomatic black Africans reported as having reduced eGFR using various eGFR equations. We further compared the association between known risk factors for CKD with eGFR determined using the different equations.

METHODS

We used participant and laboratory data collected as part of a global reference interval study conducted by the Committee of Reference Intervals and Decision Limits (C-RIDL) under the International Federation of Clinical Chemistry (IFCC). Serum creatinine values were used to calculate eGFR using the Cockcroft-Gault (CG), re-expressed 4 variable modified diet in renal disease (4v-MDRD), full age spectrum (FAS) and chronic kidney disease epidemiology collaboration equations (CKD-EPI). CKD classification based on eGFR was determined for every participant.

RESULTS

A total of 533 participants were included comprising 273 (51.2%) females. The 4v-MDRD equation without correction for race classified the least number of participants (61.7%) as having an eGFR equivalent to CKD stage G1 compared to 93.6% for CKD-EPI with correction for race. Only age had a statistically significant linear association with eGFR across all equations after performing multiple regression analysis. The multiple correlation coefficients for CKD risk factors were higher for CKD-EPI determined eGFRs.

CONCLUSIONS

This study found that eGFR determined using CKD-EPI equations better correlated with a prediction model that included risk factors for CKD and classified fewer asymptomatic black Africans as having a reduced eGFR compared to 4v-MDRD, FAS and CG corrected for body surface area.

Impact of the estimation equation for GFR on population-based prevalence estimates of kidney dysfunction

Background

Estimating equations are recommended by clinical guidelines as the preferred method for assessment of glomerular filtration rate (GFR). The aim of the study was to compare population-based prevalence estimates of decreased kidney function in Germany defined by an estimated GFR (eGFR) <60 ml/min/1.73m² using different equations.

Methods

The study included 7001 participants of the German Health Interview and Examination Survey for Adults 2008–2011 (DEGS1) for whom GFR was estimated using the Modification of Diet in Renal Disease study equation (MDRD), the revised Lund-Malmö equation (LM), the Full Age Spectrum creatinine equation (FAScre), the Chronic Kidney Disease Epidemiology Collaboration equations with creatinine and cystatin C (CKD-EPIcrecys), with creatinine (CKD-EPIcre) and with cystatin C (CKD-EPIcys). Bland-Altman plots were used to evaluate the agreement between the equations.

Results

Prevalence estimates of decreased kidney function were: 2.1% (CKD-EPIcys), 2.3% (CKD-EPIcrecys), 3.8% (CKD-EPIcre), 5.0% (MDRD), 6.0% (LM) and 6.9% (FAScre). The systematic differences between the equations were smaller by comparing either equations that include serum cystatin C or equations that include serum creatinine alone and increased considerably by increasing eGFR.

Conclusions

Prevalence estimates of decreased kidney function vary considerably according to the equation used for estimating GFR. Equations that include serum cystatin C provide lower prevalence estimates if compared with equations based on serum creatinine alone. However, the analysis of the agreement between the equations according to eGFR provides evidence that the equations may be used interchangeably among persons with pronounced decreased kidney function. The study illustrates the implications of the choice of the estimating equation in an epidemiological setting.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0749-5) contains supplementary material, which is available to authorized users.

Establishing the presence or absence of chronic kidney disease: Uses and limitations of formulas estimating the glomerular filtration rate

The development of formulas estimating glomerular filtration rate (eGFR) from serum creatinine and cystatin C and accounting for certain variables affecting the production rate of these biomarkers, including ethnicity, gender and age, has led to the current scheme of diagnosing and staging chronic kidney disease (CKD), which is based on eGFR values and albuminuria. This scheme has been applied extensively in various populations and has led to the current estimates of prevalence of CKD. In addition, this scheme is applied in clinical studies evaluating the risks of CKD and the efficacy of various interventions directed towards improving its course. Disagreements between creatinine-based and cystatin-based eGFR values and between eGFR values and measured GFR have been reported in various cohorts. These disagreements are the consequence of variations in the rate of production and in factors, other than GFR, affecting the rate of removal of creatinine and cystatin C. The disagreements create limitations for all eGFR formulas developed so far. The main limitations are low sensitivity in detecting early CKD in several subjects, e.g., those with hyperfiltration, and poor prediction of the course of CKD. Research efforts in CKD are currently directed towards identification of biomarkers that are better indices of GFR than the current biomarkers and, particularly, biomarkers of early renal tissue injury.

Evaluation of cystatin C in malignancy and comparability of estimates of GFR in oncology patients

OBJECTIVES

Creatinine is the biomarker of choice for use in estimates of kidney function in oncology patients. However as non-renal factors such as muscle mass can influence creatinine concentrations, we evaluated cystatin C as an alternative biomarker and its incorporation in GFR estimating formulae in an oncology setting. Measured GFR is infrequently undertaken in adult clinical practice with the consequent reliance on calculated GFR for patient assessment.

DESIGN AND METHODS

Cystatin C and creatinine concentrations were evaluated from 134 oncology patients prior to commencing chemotherapeutic cycles. Estimates of creatinine clearance (Cockroft-Gault) and GFR (using Hoek, Jonsson, MDRD and CKD-EPI) were evaluated. Cystatin C-based GFR estimates (using CKD-EPI CysC and CKD-EPI SCr/CysC) were compared with the creatinine-based GFR estimates (CG, MDRD and CKD-EPI SCr) within the GFR ranges of 60-89, 45-59 and ≤44 mL/min/1.73 m2.

RESULTS

Cystatin C concentrations were significantly higher in oncology patients both prior to commencing chemotherapy (F: P<0.01 and M: P<0.0001) and during cycles of treatment (F: P<0.0001 and M: P<0.01) when compared with a reference population. Cystatin C concentrations also increased significantly during chemotherapy (P<0.0001) in a subset of female patients evaluated. Poor agreement (average 42%) was demonstrated between CKD-EPI CysC and creatinine-based GFR estimates within the investigated GFR ranges, with improved agreement (average 55%) when using the combined CKD-EPI SCr/CysC formula.

CONCLUSIONS

This study demonstrated a malignancy and treatment-mediated effect on cystatin C measures, which may confound its clinical utility in estimating GFR in oncology patients.

Practical Recommendations for Long-term Management of Modifiable Risks in Kidney and Liver Transplant Recipients: A Guidance Report and Clinical Checklist by the Consensus on Managing Modifiable Risk in Transplantation (COMMIT) Group

Short-term patient and graft outcomes continue to improve after kidney and liver transplantation, with 1-year survival rates over 80%; however, improving longer-term outcomes remains a challenge. Improving the function of grafts and health of recipients would not only enhance quality and length of life, but would also reduce the need for retransplantation, and thus increase the number of organs available for transplant. The clinical transplant community needs to identify and manage those patient modifiable factors, to decrease the risk of graft failure, and improve longer-term outcomes.COMMIT was formed in 2015 and is composed of 20 leading kidney and liver transplant specialists from 9 countries across Europe. The group's remit is to provide expert guidance for the long-term management of kidney and liver transplant patients, with the aim of improving outcomes by minimizing modifiable risks associated with poor graft and patient survival posttransplant.The objective of this supplement is to provide specific, practical recommendations, through the discussion of current evidence and best practice, for the management of modifiable risks in those kidney and liver transplant patients who have survived the first postoperative year. In addition, the provision of a checklist increases the clinical utility and accessibility of these recommendations, by offering a systematic and efficient way to implement screening and monitoring of modifiable risks in the clinical setting.

Cystatin C provides a better estimate of the effect of glomerular filtration rate on serum human epididymis protein 4 concentrations

BACKGROUND

We evaluated the effect of kidney glomerular function on serum concentrations of human epididymis protein 4 (HE4) using creatinine (Cr), cystatin C (CysC) and related chronic kidney disease epidemiology collaboration (CKD-EPI) equations.

METHODS

We enrolled 101 women aged ≤56 years with a glomerular filtration rate (GFR) (estimated by CKD-EPI eGFRCr) ranging from 60 to 120 mL/min/1.73 m2, free of any disease and biological and life-style factors known to influence serum HE4 concentrations, and we measured serum Cr, CysC and HE4 concentrations. Cr and CysC values were included in the three CKD-EPI equations to obtain GFR estimates.

RESULTS

A statistically significant increase in HE4 median concentrations was detected in subjects with an eGFRCr between 60 and 74 mL/min/1.73 m2 when compared with those with an eGFR >90 mL/min/1.73 m2 (54.2 vs. 42.2 pmol/L, p=0.003). Regression models showed that CysC measurement per se and eGFRCysC were the most sensitive markers to catch HE4 increases due to a mild decrease in renal function [adjusted r2, 0.38 (p=0.00003) and 0.37 (p=0.0004), respectively]. By assuming baseline CysC and eGFRCysC at 0.80 mg/L and 101.5 mL/min/1.73 m2, an increase of 0.10 mg/L in CysC concentrations and a decrease of 10 mL/min of eGFRCysC implied an average (±SE) increase in serum HE4 concentrations of 9.2 (±1.2) and 8.8 (±1.1) pmol/L, respectively.

CONCLUSIONS

Our study shows that a better estimate of the effect of GFR on serum HE4 is obtained by measuring CysC in serum or using CKD-EPI eGFRCysC equation.

Creatinine-Based and Cystatin C-Based GFR Estimating Equations and Their Non-GFR Determinants in Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

eGFR equations have been evaluated in kidney transplant recipients with variable performance. We assessed the performance of the Modification of Diet in Renal Disease equation and the Chronic Kidney Disease Epidemiology Collaboration equations on the basis of creatinine, cystatin C, and both (eGFR creatinine-cystatin C) compared with measured GFR by iothalamate clearance and evaluated their non-GFR determinants and associations across 15 cardiovascular risk factors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cross-sectional cohort of 1139 kidney transplant recipients >1 year after transplant was analyzed. eGFR bias, precision, and accuracy (percentage of estimates within 30% of measured GFR) were assessed. Interaction of each cardiovascular risk factor with eGFR relative to measured GFR was determined.

RESULTS

Median measured GFR was 55.0 ml/min per 1.73 m(2). eGFR creatinine overestimated measured GFR by 3.1% (percentage of estimates within 30% of measured GFR of 80.4%), and eGFR Modification of Diet in Renal Disease underestimated measured GFR by 2.2% (percentage of estimates within 30% of measured GFR of 80.4%). eGFR cystatin C underestimated measured GFR by -13.7% (percentage of estimates within 30% of measured GFR of 77.1%), and eGFR creatinine-cystatin C underestimated measured GFR by -8.1% (percentage of estimates within 30% of measured GFR of 86.5%). Lower measured GFR associated with older age, women, obesity, longer time after transplant, lower HDL, lower hemoglobin, lower albumin, higher triglycerides, higher proteinuria, and an elevated cardiac troponin T level but did not associate with diabetes, smoking, cardiovascular events, pretransplant dialysis, or hemoglobin A1c. These risk factor associations differed for five risk factors with eGFR creatinine, six risk factors for eGFR Modification of Diet in Renal Disease, ten risk factors for eGFR cystatin C, and four risk factors for eGFR creatinine-cystatin C.

CONCLUSIONS

Thus, eGFR creatinine and eGFR creatinine-cystatin C are preferred over eGFR cystatin C in kidney transplant recipients because they are less biased, more accurate, and more consistently reflect the same risk factor associations seen with measured GFR.