Relative performance of the MDRD and CKD-EPI equations for estimating glomerular filtration rate among patients with varied clinical presentations

Estimating Glomerular Filtration Rate in Kidney Transplant Recipients: Comparing a Novel Equation With Commonly Used Equations in this Population

Background

Assessment of glomerular filtration rate (GFR) is important in kidney transplantation. The aim was to develop a kidney transplant specific equation for estimating GFR and evaluate against published equations commonly used for GFR estimation in these patients.

Methods

Adult kidney recipients (n = 594) were included, and blood samples were collected 10 weeks posttransplant. GFR was measured by ⁵¹Cr-ethylenediaminetetraacetic acid clearance. Patients were randomized into a reference group (n = 297) to generate a new equation and a test group (n = 297) for comparing it with 7 alternative equations.

Results

Two thirds of the test group were males. The median (2.5-97.5 percentile) age was 52 (23-75) years, cystatin C, 1.63 (1.00-3.04) mg/L; creatinine, 117 (63-220) μmol/L; and measured GFR, 51 (29-78) mL/min per 1.73 m². We also performed external evaluation in 133 recipients without the use of trimethoprim, using iohexol clearance for measured GFR. The Modification of Diet in Renal Disease equation was the most accurate of the creatinine-equations. The new equation, estimated GFR (eGFR) = 991.15 × (1.120^sex/([age^0.097] × [cystatin C^0.306] × [creatinine^0.527]); where sex is denoted: 0, female; 1, male, demonstrating a better accuracy with a low bias as well as good precision compared with reference equations. Trimethoprim did not influence the performance of the new equation.

Conclusions

The new equation demonstrated superior accuracy, precision, and low bias. The Modification of Diet in Renal Disease equation was the most accurate of the creatinine-based equations.

Contrast-induced acute kidney injury and mortality in ST elevation myocardial infarction treated with primary percutaneous coronary intervention

Objectives

Contrast-induced acute kidney injury (CI-AKI) is a common and potentially severe complication in patients with ST elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (pPCI). There is no consensus on the best definition of CI-AKI to identify patients at risk of haemodialysis or death. The objective of this study was to assess the association of CI-AKI, using four definitions, on inhospital mortality, mortality or haemodialysis requirement over 1-year follow-up, in patients with STEMI treated with pPCI.

Methods

In this prospective, observational study, all patients with STEMI referred for pPCI were included. We identified independent variables associated with CI-AKI and mortality.

Results

We included 1114 consecutive patients with STEMI treated by pPCI. CI-AKI occurred in 18.3%, 12.2%, 15.6% and 10.5% of patients according to the CIN, Acute Kidney Injury Network (AKIN), Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease (RIFLE) Modification of Diet in Renal Disease (MDRD) and RIFLE Chronic Kidney Disease - Epidemiology Collaboration (CKD-EPI) definitions, respectively. The RIFLE (CKD-EPI) definition was the most discriminant definition to identify patients at higher risk of inhospital mortality (27.1% vs 4.0%; adjusted OR 2.7 (95% CI 1.4 to 5.1), p=0.003), 1-year mortality (27.4% vs 6.6%; adjusted OR 2.8 (95% CI 1.5 to 5.3), p=0.002) and haemodialysis requirement at 1-year follow-up (15.6% vs 2.7%; adjusted OR 6.7 (95% CI 3.3 to 13.6), p=0.001). Haemodynamic instability, cardiac arrest, preexisting renal failure, elderly age and a high contrast media volume were independently associated with 1-year mortality. Of interest, contrast-media volume was not correlated to increase of creatininaemia (r=0.06) or decrease in estimated glomerular filtration rate (r=0.05) after percutaneous coronary intervention in our population.

Conclusions

CI-AKI is a frequent and serious complication of STEMI treated by pPCI. The RIFLE definition is the most accurate definition to identify patients with CI-AKI at high risk of mortality or haemodialysis.

Systematic Review and Metaanalysis Comparing the Bias and Accuracy of the Modification of Diet in Renal Disease and Chronic Kidney Disease Epidemiology Collaboration Equations in Community-Based Populations

BACKGROUND

The majority of patients with chronic kidney disease are diagnosed and monitored in primary care. Glomerular filtration rate (GFR) is a key marker of renal function, but direct measurement is invasive; in routine practice, equations are used for estimated GFR (eGFR) from serum creatinine. We systematically assessed bias and accuracy of commonly used eGFR equations in populations relevant to primary care.

CONTENT

MEDLINE, EMBASE, and the Cochrane Library were searched for studies comparing measured GFR (mGFR) with eGFR in adult populations comparable to primary care and reporting both the Modification of Diet in Renal Disease (MDRD) and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations based on standardized creatinine measurements. We pooled data on mean bias (difference between eGFR and mGFR) and on mean accuracy (proportion of eGFR within 30% of mGFR) using a random-effects inverse-variance weighted metaanalysis. We included 48 studies of 26875 patients that reported data on bias and/or accuracy. Metaanalysis of within-study comparisons in which both formulae were tested on the same patient cohorts using isotope dilution-mass spectrometry-traceable creatinine showed a lower mean bias in eGFR using CKD-EPI of 2.2 mL/min/1.73 m² (95% CI, 1.1-3.2; 30 studies; I² = 74.4%) and a higher mean accuracy of CKD-EPI of 2.7% (1.6-3.8; 47 studies; I² = 55.5%). Metaregression showed that in both equations bias and accuracy favored the CKD-EPI equation at higher mGFR values.

SUMMARY

Both equations underestimated mGFR, but CKD-EPI gave more accurate estimates of GFR.

Predictors of Perioperative Acute Kidney Injury in Obese Patients Undergoing Laparoscopic Bariatric Surgery: a Single-Centre Retrospective Cohort Study

BACKGROUND

Obesity has been associated with increased risk of perioperative acute kidney injury (AKI). We aim to establish the incidence of AKI among patients undergoing laparoscopic bariatric surgery and identify potential risk factors.

METHODS

Records of 1230 patients who underwent laparoscopic bariatric surgery in a tertiary centre from 1 December 2009 to 31 January 2014 were retrospectively studied. AKI diagnosis was made by comparing the baseline and post-operative serum creatinine to determine the presence of predefined significant change based on the Kidney Disease: Improving Global Outcomes (KDIGO) definition. Univariate analyses were performed to determine significant clinical factors, and multiple logistic regression analysis was subsequently done to determine independent predictors of AKI.

RESULTS

Thirty-five (2.9 %) patients developed AKI during the first 72 h post-surgery. Multivariate logistic regression analysis revealed impaired renal function (OR 10.429, 95 % CI 3.560 to 30.552), use of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers (OR 3.038, 95 % CI 1.352 to 6.824), and body mass index (OR 1.048, 95 % CI 1.005 to 1.093) as independent predictors of perioperative acute kidney injury in the obese patients who underwent laparoscopic bariatric surgery.

CONCLUSIONS

We found that the incidence of perioperative AKI among patients who underwent laparoscopic bariatric surgery is at 2.9 %. Impaired renal function, use of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers and raised body mass index were found to be independent predictors of AKI. Patients with these risk factors could be considered at risk for developing perioperative AKI, and extra perioperative vigilance should be undertaken.

Rethinking CKD Evaluation: Should We Be Quantifying Basal or Stimulated GFR to Maximize Precision and Sensitivity?

Chronic kidney disease (CKD) is an increasing clinical problem. Although clinical risk factors and biomarkers for the development and progression of CKD have been identified, there is no commercial surveillance technology to definitively diagnose and quantify the severity and progressive loss of glomerular filtration rate (GFR) in CKD. This has limited the study of potential therapies to late stages of CKD when FDA-registerable events are more likely. Because patient outcomes, including the rate of CKD progression, correlate with disease severity and effective therapy may require early intervention, being able to diagnose and stratify patients by their level of decreased kidney function early on is key for translational progress. In addition, renal reserve, defined as the increase in GFR following stimulation, may improve the quantification of GFR based solely on basal levels. Various groups are developing and characterizing optical measurement techniques using new minimally invasive or noninvasive approaches for quantifying basal and stimulated kidney function. This development has the potential to allow widespread individualization of therapy at an earlier disease stage. Therefore, the purposes of this review are to suggest why quantifying stimulated GFR, by activating renal reserve, may be advantageous in patients and to review fluorescent technologies to deliver patient-specific GFR.

Impact of Renal Functional/Morphological Dynamics on the Calcification of Coronary and Abdominal Arteries in Patients with Chronic Kidney Disease

Aim: Fast-progressing vascular calcification (VC) is accompanied by renal atrophy and functional deterioration along with atherosclerosis in patients with chronic kidney disease (CKD). However, the relationship between VC progression and renal functional and/or morphological changes remains unclear.

Methods: We included 70 asymptomatic patients with CKD without hemodialysis in our study. To identify temporal variations, the coronary artery calcification score (CACS), abdominal aortic calcification index (ACI), and renal parenchymal volume index (RPVI) were determined via spiral computed tomography scans taken during the study. We investigated significant factors related to annualized variations of CACS (ΔCACS/y) and ACI (ΔACI/y).

Results: During the follow-up period (4.6 years), median values of CACS [in Agatston units (AU)] and ACI increased from 40.2 to 113.3 AU (p = 0.053) and from 13.2 to 21.7% (p = 0.036), respectively. Multivariate analysis revealed that CACS at baseline (p < 0.001) and diabetes mellitus (DM) status (p = 0.037) for ΔCACS/y and ACI at baseline (p = 0.017) and hypertension (HT) status (p = 0.046) for ΔACI/y were significant independent predictors. Furthermore, annualized RPVI variation was significantly related to both ΔCACS/y and ΔACI/y (R = −0.565, p < 0.001, and R = −0.289, p = 0.015, respectively). On the other hand, independent contributions of the estimated glomerular filtration rate (eGFR) and annualized eGFR variation to VC progression were not confirmed.

Conclusion: The degree of VC at baseline, DM, HT, and changes in renal volume, but not eGFR, had a strong impact on VC progression in patients with CKD.

Accuracy diagrams: a novel way to illustrate uncertainty of estimated GFR

Most studies that validate GFR equations present accuracy results stratified by measured GFR (mGFR; diagnostic correctness) or by estimated GFR (eGFR; diagnostic predictiveness) only, without a clear distinction in interpretation. The accuracy of a GFR equation is normally reported in percent (e.g. P₃₀), but is often misinterpreted when stratified by eGFR. The aim of the study was to develop new accuracy measures and diagrams that allow straightforward interpretations and illustrations of the uncertainty in eGFR in clinical practice. We applied quantile regression to the distribution of estimation errors for two creatinine-based GFR equations, LM-REV and CKD-EPI, in a clinical cohort (n = 3495) referred for GFR measurement (plasma clearance of iohexol). Measures of bias and precision and accuracy intervals (AIs) were expressed in mL/min/1.73 m². Diagrams with AIs were chosen as a novel way to present the error margin in eGFR at a pre-specified certainty level. It was shown that creatinine-based equations are still quite inaccurate in that large estimation errors could not be ruled out with satisfactory certainty. As an example, the 75% AI for the most accurate equation, LM-REV, was approximately ±10 mL/min/1.73 m² at eGFR = 45 mL/min/1.73 m², whereas it ranged between -13 and +20 mL/min/1.73 m² at eGFR = 90 mL/min/1.73 m². Accuracy intervals presented in diagrams can be used to illustrate the uncertainty of eGFR. Future validation studies should assess the variability in the predictiveness of eGFR across populations and clinical settings using tools and performance measures that are easy to interpret.

Quantifying Glomerular Filtration Rates in Acute Kidney Injury: A Requirement for Translational Success

Acute kidney injury (AKI) remains a vexing clinical problem that results in unacceptably high patient mortality, development of chronic kidney disease, and accelerated progression to end-stage kidney disease. Although clinical risks factors for developing AKI have been identified, there is no reasonable surveillance technique to definitively and rapidly diagnose and determine the extent of severity of AKI in any patient. Because patient outcomes correlate with the extent of injury, and effective therapy likely requires early intervention, the ability to rapidly diagnose and stratify patients by their level of kidney injury is paramount for translational progress. Many groups are developing and characterizing optical measurement techniques using novel minimally invasive or noninvasive techniques that can quantify kidney function independent of serum or urinary measurements. The use of both one- and two-compartment models, as well as continuous monitoring, are being developed. This review documents the need for glomerular filtration rate measurement in AKI patients and discusses the approaches being taken to deliver this overdue technique that is necessary to help propel nephrology to individualization of care and therapeutic success.

Successful Pregnancies in Kidney Transplant Recipients: Experience of the National Kidney Transplant Program From Uruguay

BACKGROUND

Renal transplantation increases the possibilities of pregnancy in women of reproductive age. The course of pregnancy was analyzed retrospectively in patients with kidney or kidney-pancreas transplant, surveying maternal-fetal or renal graft complications and the relation with pre-pregnancy renal function.

METHODS

A cohort that includes all the kidney transplant recipients who went through pregnancy in Uruguay in a period of 28 years is described. Forty pregnancies in 32 patients were registered; the average time between the kidney transplant and the beginning of the gestation period was 47 months. From the total gestations, 10 abortions, 1 neonatal death, and 1 fetal demise were registered. From the remaining pregnancies, we highlight prematurity (18/29) and low birth weight (14/21). Twenty-nine in 30 pregnancies ended in cesarean section; in 8 of 30, pre-eclampsia diagnosis was performed. Acute rejection was diagnosed in 2 of 30 pregnancies, both undergoing their first post-transplant year.

RESULTS

Two patients required dialysis throughout the pregnancy because of progress into severe renal insufficiency. Higher obstetric perinatal morbidity and renal function deterioration was related to lower pre-pregnancy glomerular filtration rate (GFR).

CONCLUSIONS

A successful pregnancy is possible in transplant recipients, yet there are risks of prematurity, low birth weight, and abortion. A lower GFR before pregnancy was associated with poorer maternal and perinatal results as shown in the different series.

Metabolic and Hormonal Determinants of Glomerular Filtration Rate and Renal Hemodynamics in Severely Obese Individuals

OBJECTIVE

Renal function is often compromised in severe obesity. A true measurement of glomerular filtration rate (GFR) is unusual, and how estimation formulae (EstForm) perform in such individuals is unclear. We characterized renal function and hemodynamics in severely obese individuals, assessing the reliability of EstForm.

METHODS

We measured GFR (mGFR) by iohexol plasma clearance, renal plasma flow (RPF) by 123I-ortho-iodo-hippurate, basal and stimulated vascular renal indices, endothelium-dependent and -independent vasodilation using flow-mediated dilation (FMD) as well as metabolic and hormonal profile in morbid, otherwise healthy, obese subjects.

RESULTS

Compared with mGFR, the better performing EstForm was CKD-EPI (5.3 ml/min/1.73 m2 bias by Bland-Altman analysis). mGFR was directly related with RPF, total and incremental glucose AUC, and inversely with PTH and h8 cortisol. Patients with mGFR below the median shown significantly higher PTH and lower vitamin D3. Basal or dynamic renal resistive index, FMD, pulse wave velocity were not related with mGFR. In an adjusted regression model, renal diameter and plasma flow remained related with mGFR (R2 = 0.67), accounting for 15% and 21% of mGFR variance, respectively.

CONCLUSIONS

CKD-EPI formula should be preferred in morbid obesity; glucose increments during oral glucose tolerance test correlate with hyperfiltration; RPF and diameter are independent determinants of mGFR; slightly high PTH values, frequent in obesity, might influence mGFR.

Structural and Functional Changes With the Aging Kidney

Senescence or normal physiologic aging portrays the expected age-related changes in the kidney as compared to a disease that occurs in some but not all individuals. The microanatomical structural changes of the kidney with older age include a decreased number of functional glomeruli from an increased prevalence of nephrosclerosis (arteriosclerosis, glomerulosclerosis, and tubular atrophy with interstitial fibrosis), and to some extent, compensatory hypertrophy of remaining nephrons. Among the macroanatomical structural changes, older age associates with smaller cortical volume, larger medullary volume until middle age, and larger and more numerous kidney cysts. Among carefully screened healthy kidney donors, glomerular filtration rate (GFR) declines at a rate of 6.3 mL/min/1.73 m(2) per decade. There is reason to be concerned that the elderly are being misdiagnosed with CKD. Besides this expected kidney function decline, the lowest risk of mortality is at a GFR of ≥75 mL/min/1.73 m(2) for age <55 years but at a lower GFR of 45 to 104 mL/min/1.73 m(2) for age ≥65 years. Changes with normal aging are still of clinical significance. The elderly have less kidney functional reserve when they do actually develop CKD, and they are at higher risk for acute kidney injury.

Chronic Kidney Disease Classification in Systolic Blood Pressure Intervention Trial: Comparison Using Modification of Diet in Renal Disease and CKD-Epidemiology Collaboration Definitions

BACKGROUND

Interventional trials have used either the Modification of Diet in Renal Disease (MDRD) or chronic kidney disease (CKD)-Epidemiology Collaboration (CKD-EPI) equation for determination of estimated glomerular filtration rate (eGFR) to define whether participants have stages 3-5 CKD. The equation used to calculate eGFR may influence the number and characteristics of participants designated as having CKD.

METHODS

We examined the classification of CKD at baseline using both equations in the Systolic Blood Pressure Intervention Trial (SPRINT). eGFR was calculated at baseline using fasting serum creatinine values from a central laboratory.

RESULTS

Among 9,308 participants with baseline CKD classification using the 4-variable MDRD equation specified in the SPRINT protocol, 681 (7.3%) participants were reclassified to a less advanced CKD stage (higher eGFR) and 346 (3.7%) were reclassified to a more advanced CKD stage (lower eGFR) when the CKD-EPI equation was used to calculate eGFR. For eGFRs <90 ml/min/1.73 m2, participants <75 years were more likely to be reclassified to a less advanced CKD stage; this reclassification was more likely to occur in non-blacks rather than blacks. Participants aged ≥75 years were more likely to be reclassified to a more advanced than a less advanced CKD stage, regardless of baseline CKD stage. Reclassification of baseline CKD status (eGFR <60 ml/min/1.73 m2) occurred in 3% of participants.

CONCLUSIONS

Use of the MDRD equation led to a higher percentage of participants being classified as having CKD stages 3-4. Younger and non-black participants were more likely to be reclassified as not having CKD using the CKD-EPI equation.

The renal effects of ALK inhibitors

Anaplastic lymphoma kinase 1 (ALK-1) is a member of the insulin receptor tyrosine kinase family. In clinical practice, three small molecule inhibitors of ALK-1 are used, namely crizotinib, ceritinib and alectinib. Several more agents are in active pre-clinical and clinical studies. Crizotinib is approved for the treatment of advanced ALK-positive non-small cell lung cancer (NSCLC). According to the package insert and published literature, treatment with crizotinib appears to be associated with kidney failure as well as an increased risk for the development and progression of renal cysts. In addition, this agent is associated with development of peripheral edema and rare electrolyte disorders. This review focuses on the adverse renal effects of Crizotinib in clinical practice.

Validation of the Korean coefficient for the modification of diet in renal disease study equation

BACKGROUND/AIMS

Race and ethnicity are important determinants when estimatingglomerular filtration rate (GFR). The Korean coefficients for the isotope dilution mass spectrometry (IDMS) Modification of Diet in Renal Disease (MDRD) Study equations were developed in 2010. However, the coefficients have not been validated. The aim of this study was to validate the performance of the Korean coefficients for the IDMS MDRD Study equations.

METHODS

Equation development and validation were performed in separate groups (development group, n = 147 from 2008 to 2009; validation group, n = 125 from 2010 to 2012). We compared the performance of the original IDMS MDRD equations and modified equations with Korean coefficients. Performance was assessed by comparing correlation coefficients, bias, and accuracy between estimated GFR and measured GFR, with systemic inulin clearance using a single injection method.

RESULTS

The Korean coefficients for the IDMS MDRD equations developed previously showed good performance in the validation group. The new Korean coefficients for the four- and six-variable IDMS MDRD equations using both the development and validation cohorts were 1.02046 and 0.97300, respectively. No significant difference was detected for the new Korean coefficients, in terms of estimating GFR, between the original and modified IDMS MDRD Study equations.

CONCLUSIONS

The modified equations with Korean coefficients for the IDMS MDRD Study equations were not superior to the original equations for estimating GFR. Therefore, we recommend using the original IDMS MDRD Study equation without ethnic adjustment in the Korean population.

Cystatin C- and Creatinine-Based Estimates of Glomerular Filtration Rate in Dapagliflozin Phase 3 Clinical Trials

INTRODUCTION

To compare estimated glomerular filtration rate measured by serum creatinine (eGFRcr) and serum cystatin C (eGFRcys) in patients with type 2 diabetes mellitus from dapagliflozin clinical trials.

METHODS

Post hoc analysis of data pooled from 9 phase 3, randomized, placebo-controlled, 24-week trials of dapagliflozin. The correlation between eGFRcr and eGFRcys was modeled by a simple linear regression. The proportions of patients with eGFR 30 to <60 and ≥60 mL/min/1.73 m(2) based on creatinine versus cystatin C were compared.

RESULTS

Of 4745 total patients, 4294 (90.5%) had serum cystatin C data available for calculation of eGFRcys. The correlation between eGFRcr and eGFRcys was poor (R (2) = 30%). Of patients with eGFRcr 30 to <60 mL/min/1.73 m(2), 66% had eGFR ≥60 when recalculated based on cystatin C. Among patients with eGFRcr ≥60 mL/min/1.73 m(2), 95.8% had eGFR ≥60 when estimated using cystatin C. Decreases in HbA1c, body weight, and systolic blood pressure with dapagliflozin were similar among patient subgroups defined by either eGFR estimate and were statistically significant and clinically meaningful with dapagliflozin 10 mg/day in most subgroups.

CONCLUSION

The correlation between eGFRcr and eGFRcys was poor. Renal function assessed by eGFRcr may be underestimated, and some patients may be misdiagnosed with chronic kidney disease and/or unjustifiably deemed ineligible for certain antidiabetes medications. This is in consonance with guidelines suggesting using eGFRcys as a confirmatory measure when eGFRcr is between 45 and <60 mL/min/1.73 m(2) with no evidence of kidney damage and/or in other situations where eGFRcr may be unreliable.

FUNDING

AstraZeneca.

Comparison of the Schwartz and CKD-EPI Equations for Estimating Glomerular Filtration Rate in Children, Adolescents, and Adults: A Retrospective Cross-Sectional Study

BACKGROUND

Estimating kidney glomerular filtration rate (GFR) is of utmost importance in many clinical conditions. However, very few studies have evaluated the performance of GFR estimating equations over all ages and degrees of kidney impairment. We evaluated the reliability of two major equations for GFR estimation, the CKD-EPI and Schwartz equations, with urinary clearance of inulin as gold standard.

METHODS AND FINDINGS

The study included 10,610 participants referred to the Renal and Metabolic Function Exploration Unit of Edouard Herriot Hospital (Lyon, France). GFR was measured by urinary inulin clearance (only first measurement kept for analysis) then estimated with isotope dilution mass spectrometry (IDMS)-traceable CKD-EPI and Schwartz equations. The participants' ages ranged from 3 to 90 y, and the measured GFRs from 3 to 160 ml/min/1.73 m2. A linear mixed-effects model was used to model the bias (mean ratio of estimated GFR to measured GFR). Equation reliability was also assessed using precision (interquartile range [IQR] of the ratio) and accuracy (percentage of estimated GFRs within the 10% [P10] and 30% [P30] limits above and below the measured GFR). In the whole sample, the mean ratio with the CKD-EPI equation was significantly higher than that with the Schwartz equation (1.17 [95% CI 1.16; 1.18] versus 1.08 [95% CI 1.07; 1.09], p < 0.001, t-test). At GFR values of 60-89 ml/min/1.73 m2, the mean ratios with the Schwartz equation were closer to 1 than the mean ratios with the CKD-EPI equation whatever the age class (1.02 [95% CI 1.01; 1.03] versus 1.15 [95% CI 1.13; 1.16], p < 0.001, t-test). In young adults (18-40 y), the Schwartz equation had a better precision and was also more accurate than the CKD-EPI equation at GFR values under 60 ml/min/1.73 m2 (IQR: 0.32 [95% CI 0.28; 0.33] versus 0.40 [95% CI 0.36; 0.44]; P30: 81.4 [95% CI 78.1; 84.7] versus 63.8 [95% CI 59.7; 68.0]) and also at GFR values of 60-89 ml/min/1.73 m2. In all patients aged ≥65 y, the CKD-EPI equation performed better than the Schwartz equation (IQR: 0.33 [95% CI 0.31; 0.34] versus 0.40 [95% CI 0.38; 0.41]; P30: 77.6 [95% CI 75.7; 79.5] versus 67.5 [95% CI 65.4; 69.7], respectively). In children and adolescents (2-17 y), the Schwartz equation was superior to the CKD-EPI equation (IQR: 0.23 [95% CI 0.21; 0.24] versus 0.33 [95% CI 0.31; 0.34]; P30: 88.6 [95% CI 86.7; 90.4] versus 29.4 [95% CI 26.8; 32.0]). This study is limited by its retrospective design, single-center setting with few non-white patients, and small number of patients with severe chronic kidney disease.

CONCLUSIONS

The results from this study suggest that the Schwartz equation may be more reliable than the CKD-EPI equation for estimating GFR in children and adolescents and in adults with mild to moderate kidney impairment up to age 40 y.

Evaluation of creatinine-based and cystatin C-based equations for estimation of glomerular filtration rate in type 1 diabetic patients

Objective Several formulas based in different biomarkers may be used to estimate glomerular filtration rate (GRF). However, all of them have some limitations, and it is very important to evaluate their performances in different groups of patients. Therefore, we compared GFR, as estimated by creatinine-based and cystatin C-based equations, according to albuminuria, in type 1 diabetes (T1DM), in an observational case-control study. Subjects and methods T1DM patients were classified according to albuminuria: normoalbuminuric (n = 63), microalbuminuric (n = 30), macroalbuminuric (n = 32). GFR was calculated using creatinine-based and cystatin C-based (aMDRD, CKD-EPIcr, CKD-EPIcys, MacIsaac, Tan and CKD-EPIcrcys) equations. Spearman Correlation was used to evaluate the correlation of GFR estimated by the formulas with albuminuria. ROC curves were constructed to compare AUCs of GFR estimated by equations, in reference to macroalbuminuria. Sensibility, specificity and accuracy were calculated for a cut-off < 60 mL/min/1.73 m2. Results GFR estimated by creatinine-based and cystatin C-based equations significantly differed among normoalbuminuric, microalbuminuric and macroalbuminuric patients. Spearman correlation and AUCs of GFR estimated by creatinine-based and cystatin C-based formulas were very similar to each other, though cystatin C-based equations presented better correlation with albuminuria and higher AUCs than the creatinine-based ones, and the best accuracy to detect macroalbuminuric patients. Conclusion Although GFR estimated by all creatinine-based and cystatin C-based equations permitted the differentiation between T1DM patients, according to albuminuria, cystatin C-based equations presented best accuracy to detect macroalbuminuria in T1DM patients and should be considered in the clinical routine in order to increase the possibility of early diagnostic of chronic renal disease.

Structural and Functional Changes With the Aging Kidney

Senescence or normal physiologic aging portrays the expected age-related changes in the kidney as compared to a disease that occurs in some but not all individuals. The microanatomical structural changes of the kidney with older age include a decreased number of functional glomeruli from an increased prevalence of nephrosclerosis (arteriosclerosis, glomerulosclerosis, and tubular atrophy with interstitial fibrosis), and to some extent, compensatory hypertrophy of remaining nephrons. Among the macroanatomical structural changes, older age associates with smaller cortical volume, larger medullary volume until middle age, and larger and more numerous kidney cysts. Among carefully screened healthy kidney donors, glomerular filtration rate (GFR) declines at a rate of 6.3 mL/min/1.73 m(2) per decade. There is reason to be concerned that the elderly are being misdiagnosed with CKD. Besides this expected kidney function decline, the lowest risk of mortality is at a GFR of ≥75 mL/min/1.73 m(2) for age <55 years but at a lower GFR of 45 to 104 mL/min/1.73 m(2) for age ≥65 years. Changes with normal aging are still of clinical significance. The elderly have less kidney functional reserve when they do actually develop CKD, and they are at higher risk for acute kidney injury.

The Chronic Kidney Disease Epidemiology Collaboration equation improves the detection of hyperfiltration in Chinese diabetic patients

OBJECTIVE

Hyperfiltration confers an increased risk of diabetic nephropathy. Early detection can ensure timely intervention and improved treatment outcomes. Because GFR is known to be affected by hyperglycemia, the aim of this study was to compare the influence of hyperglycemia on GFR estimations calculated by the CKD-EPI equation, the CG equation, and the MDRD equations in estimating hyperfiltration in Chinese diabetic patients.

MATERIALS AND METHODS

The performance of the equations, compared with the measured (99)mTc-DTPA glomerular filtration rate was analyzed in 3492 diabetic patients. Bias, precision, and accuracies were compared with respect to HbA1c status. The Bland-Altman method was used to evaluate the agreement among the equations with respect to the mGFR, and the receiver-operating characteristic curve method was used to evaluate diagnostic value of the three equations with respect to the detection of moderate renal failure and hyperfiltration.

RESULTS

The mean absolute bias was the smallest for the CKD-EPI equation in the HbA1c < 7.2% cohort, and the highest accuracy within ± 15% and ± 30% was also reached with the CKD-EPI equation in both cohorts. For the detection of hyperfiltration, the CKD-EPI equation exhibited the best performance with the greatest combination of sensitivity and specificity. The biases of the three equations were significantly higher in the HbA1c ≥ 10.5% subgroup compared with the HbA1c < 7.2% cohort.

CONCLUSION

The CKD-EPI equation can be used as a screening tool for hyperfiltration and appears to be a more generalizable and accurate equation for estimating GFR in Chinese diabetic patients.

Crizotinib effects on creatinine and non-creatinine-based measures of glomerular filtration rate

INTRODUCTION

Rapid reductions in creatinine-based estimates of the glomerular filtration rate (GFR) have recently been reported secondary to crizotinib use. Whether these reflect drug-induced changes in the true GFR or the validity of creatinine as a measure of kidney function in the presence of crizotinib is unknown.

METHODS

Two anaplastic lymphoma kinase-rearranged non-small-cell lung cancer patients (one with pre-existing renal impairment) were identified during periods of time on and off crizotinib. Creatinine- and iothalamate-based estimates of renal function were conducted in the presence and absence of crizotinib.

RESULTS

Crizotinib is associated with both acute and chronic effects on kidney function. Chronic creatinine changes seem to reflect a true reduction in the GFR. In contrast, acute effects include a reduction in creatinine-based estimates of the GFR without a reduction in non-creatinine-based measurements (consistent with, e.g., an acute effect of crizotinib on creatinine secretion), in addition to some reduction in the true GFR (with this latter effect seeming to be more prominent in the presence of pre-existing renal impairment).

CONCLUSION

If crizotinib-associated changes in creatinine-based kidney function suggest a change in dosing with either crizotinib or concomitant medications that are renally excreted, use of a non-creatinine-based assessment of kidney function, such as iothalamate assessments, should be considered before making a final decision.

[Dosing adjustment and renal function: Which equation(s)?]

While the CKD-EPI (for Chronic Kidney Disease Epidemiology) equation is now implemented worldwide, utilization of the Cockcroft formula is still advocated by some physicians for drug dosage adjustment. Justifications for this recommendation are that the Cockcroft formula was preferentially used to determine dose adjustments according to renal function during the development of many drugs, better predicts drugs-related adverse events and decreases the risk of drug overexposure in the elderly. In this opinion paper, we discuss the weaknesses of the rationale supporting the Cockcroft formula and endorse the French HAS (Haute Autorité de santé) recommendation regarding the preferential use of the CKD-EPI equation. When glomerular filtration rate (GFR) is estimated in order to adjust drug dosage, the CKD-EPI value should be re-expressed for the individual body surface area (BSA). Given the difficulty to accurately estimate GFR in the elderly and in individuals with extra-normal BSA, we recommend to prescribe in priority monitorable drugs in those populations or to determine their "true" GFR using a direct measurement method.

Troponin T as a Predictor of End-Stage Renal Disease and All-Cause Death in African Americans and Whites From Hypertensive Families

OBJECTIVE

To evaluate cardiac troponin T (cTnT) as a predictor of end-stage renal disease (ESRD) and death in a cohort of African American and white community-dwelling adults with hypertensive families.

PATIENTS AND METHODS

A total of 3050 participants (whites from Rochester, Minnesota; African Americans from Jackson, Mississippi) of the Genetic Epidemiology Network of Arteriopathy study were followed from baseline examination (June 1, 1996, through August 31, 2000) through January 22, 2010. Cox proportional hazards regression models were used to examine the association of cTnT with ESRD and death after adjusting for traditional risk factors.

RESULTS

Cohort demographic characteristics and measurements included 1395 whites (45.7%), 2174 hypertensive (71.3%), 992 estimated glomerular filtration rate of less than 60 mL/min per 1.73 m(2) (32.5%), 1574 high-sensitivity C-reactive protein level of greater than 3 mg/L (51.6%), and 66 abnormal cTnT level of 0.01 ng/mL or higher (2.2%). The estimated cumulative incidence of ESRD at 10 years was 27.4% among those with abnormal cTnT levels compared with 1.3% for those with normal levels. Similarly, the estimated cumulative incidence of death at 10 years was 47% among those with abnormal cTnT compared with 7.3% among those with normal cTnT. Abnormal cTnT levels were strongly associated with ESRD and death. This effect was attenuated but was still highly significant after adjustment for demographic characteristics, estimated glomerular filtration rate, and traditional risk factors for ESRD (unadjusted hazard ratio [HR], 23.91; 95% CI, 12.9-44.2; adjusted HR, 2.81; 95% CI, 1.3-5.9) and death (unadjusted HR, 8.43; 95% CI, 6.0-11.9; adjusted HR, 3.46; 95% CI, 2.3-5.1).

CONCLUSION

Cardiac troponin T makes an independent contribution to the prediction of ESRD and all-cause death in community-dwelling individuals beyond traditional risk markers. Further studies may be needed to determine whether cTnT screening in individuals with hypertension or in a subset of hypertensive individuals would help identify those at risk of ESRD and all-cause death.

Heat stress, dehydration, and kidney function in sugarcane cutters in El Salvador--A cross-shift study of workers at risk of Mesoamerican nephropathy

BACKGROUND

An epidemic of progressive kidney failure afflicts sugarcane workers in Central America. Repeated high-intensity work in hot environments is a possible cause.

OBJECTIVES

To assess heat stress, dehydration, biomarkers of renal function and their possible associations. A secondary aim was to evaluate the prevalence of pre-shift renal damage and possible causal factors.

METHODS

Sugarcane cutters (N=189, aged 18-49 years, 168 of them male) from three regions in El Salvador were examined before and after shift. Cross-shift changes in markers of dehydration and renal function were examined and associations with temperature, work time, region, and fluid intake were assessed. Pre-shift glomerular filtration rate was estimated (eGFR) from serum creatinine.

RESULTS

The mean work-time was 4 (1.4-11) hours. Mean workday temperature was 34-36 °C before noon, and 39-42 °C at noon. The mean liquid intake during work was 0.8L per hour. There were statistically significant changes across shift. The mean urine specific gravity, urine osmolality and creatinine increased, and urinary pH decreased. Serum creatinine, uric acid and urea nitrogen increased, while chloride and potassium decreased. Pre-shift serum uric acid levels were remarkably high and pre-shift eGFR was reduced (<60 mL/min) in 23 male workers (14%).

CONCLUSIONS

The high prevalence of reduced eGFR, and the cross-shift changes are consistent with recurrent dehydration from strenuous work in a hot and humid environment as an important causal factor. The pathophysiology may include decreased renal blood flow, high demands on tubular reabsorption, and increased levels of uric acid.

Diabetic Nephropathy: New Risk Factors and Improvements in Diagnosis

Diabetic nephropathy is the leading cause of end-stage renal disease. Patients with diabetic nephropathy have a high cardiovascular risk, comparable to patients with coronary heart disease. Accordingly, identification and management of risk factors for diabetic nephropathy as well as timely diagnosis and prompt management of the condition are of paramount importance for effective treatment. A variety of risk factors promotes the development and progression of diabetic nephropathy, including elevated glucose levels, long duration of diabetes, high blood pressure, obesity, and dyslipidemia. Most of these risk factors are modifiable by antidiabetic, antihypertensive, or lipid-lowering treatment and lifestyle changes. Others such as genetic factors or advanced age cannot be modified. Therefore, the rigorous management of the modifiable risk factors is essential for preventing and delaying the decline in renal function. Early diagnosis of diabetic nephropathy is another essential component in the management of diabetes and its complications such as nephropathy. New markers may allow earlier diagnosis of this common and serious complication, but further studies are needed to clarify their additive predictive value, and to define their cost-benefit ratio. This article reviews the most important risk factors in the development and progression of diabetic nephropathy and summarizes recent developments in the diagnosis of this disease.

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

BACKGROUND

The Kidney Disease Improving Global Outcomes (KDIGO) guideline recommends use of a cystatin C-based estimated glomerular filtration rate (eGFR) to confirm creatinine-based eGFR between 45 and 59 mL · min(-1) · (1.73 m(2))(-1). Prior studies have demonstrated that comorbidities such as solid-organ transplant strongly influence the relationship between measured GFR, creatinine, and cystatin C. Our objective was to evaluate the performance of cystatin C-based eGFR equations compared with creatinine-based eGFR and measured GFR across different clinical presentations.

METHODS

We compared the performance of the CKD-EPI 2009 creatinine-based estimated GFR equation (eGFRCr) and the newer CKD-EPI 2012 cystatin C-based equations (eGFRCys and eGFRCr-Cys) with measured GFR (iothalamate renal clearance) across defined patient populations. Patients (n = 1652) were categorized as transplant recipients (n = 568 kidney; n = 319 other organ), known chronic kidney disease (CKD) patients (n = 618), or potential kidney donors (n = 147).

RESULTS

eGFRCr-Cys showed the most consistent performance across different clinical populations. Among potential kidney donors without CKD [stage 2 or higher; eGFR >60 mL · min(-1) · (1.73 m(2))(-1)], eGFRCys and eGFRCr-Cys demonstrated significantly less bias than eGFRCr; however, all 3 equations substantially underestimated GFR when eGFR was <60 mL · min(-1) · (1.73 m(2))(-1). Among transplant recipients with CKD stage 3B or greater [eGFR <45 mL · min(-1) · (1.73 m(2))(-1)], eGFRCys was significantly more biased than eGFRCr. No clear differences in eGFR bias between equations were observed among known CKD patients regardless of eGFR range or in any patient group with a GFR between 45 and 59 mL · min(-1) · (1.73 m(2))(-1).

CONCLUSIONS

The performance of eGFR equations depends on patient characteristics that are readily apparent on presentation. Among the 3 CKD-EPI equations, eGFRCr-Cys performed most consistently across the studied patient populations.

Early chronic kidney disease: diagnosis, management and models of care

Chronic kidney disease (CKD) is prevalent in many countries, and the costs associated with the care of patients with end-stage renal disease (ESRD) are estimated to exceed US$1 trillion globally. The clinical and economic rationale for the design of timely and appropriate health system responses to limit the progression of CKD to ESRD is clear. Clinical care might improve if early-stage CKD with risk of progression to ESRD is differentiated from early-stage CKD that is unlikely to advance. The diagnostic tests that are currently used for CKD exhibit key limitations; therefore, additional research is required to increase awareness of the risk factors for CKD progression. Systems modelling can be used to evaluate the impact of different care models on CKD outcomes and costs. The US Indian Health Service has demonstrated that an integrated, system-wide approach can produce notable benefits on cardiovascular and renal health outcomes. Economic and clinical improvements might, therefore, be possible if CKD is reconceptualized as a part of primary care. This Review discusses which early CKD interventions are appropriate, the optimum time to provide clinical care, and the most suitable model of care to adopt.

Metabolic biomarkers for chronic kidney disease

Chronic kidney disease (CKD) is an increasingly recognized burden for patients and health care systems with high (and growing) global incidence and prevalence, significant mortality, and disproportionately high treatment costs. Yet, the available diagnostic tools are either impractical in clinical routine or have serious shortcomings impeding a well-informed disease management although optimized treatment strategies with proven benefits for the patients have become available. Advances in bioanalytical technologies have facilitated studies that identified genomic, proteomic, and metabolic biomarker candidates, and confirmed some of them in independent cohorts. This review summarizes the CKD-related markers discovered so far, and focuses on compounds and pathways, for which there is quantitative data, substantiating evidence from translational research, and a mechanistic understanding of the processes involved. Also, multiparametric marker panels have been suggested that showed promising diagnostic and prognostic performance in initial analyses although the data basis from prospective trials is very limited. Large-scale studies, however, are underway and will provide the information for validating a set of parameters and discarding others. Finally, the path from clinical research to a routine application is discussed, focusing on potential obstacles such as the use of mass spectrometry, and the feasibility of obtaining regulatory approval for targeted metabolomics assays.

Measurement of renal function in a kidney donor: a comparison of creatinine-based and volume-based GFRs

OBJECTIVE

We aimed to evaluate the performance of various GFR estimates compared with direct measurement of GFR (dGFR). We also sought to create a new formula for volume-based GFR (new-vGFR) using kidney volume determined by CT.

MATERIALS AND METHODS

GFR was measured using creatinine-based methods (MDRD, the Cockcroft-Gault equation, CKD-EPI formula, and the Mayo clinic formula) and the Herts method, which is volume-based (vGFR). We compared performance between GFR estimates and created a new vGFR model by multiple linear regression analysis.

RESULTS

Among the creatinine-based GFR estimates, the MDRD and C-G equations were similarly associated with dGFR (correlation and concordance coefficients of 0.359 and 0.369 and 0.354 and 0.318, respectively). We developed the following new kidney volume-based GFR formula: 217.48-0.39XA + 0.25XW-0.46XH-54.01XsCr + 0.02XV-19.89 (if female) (A = age, W = weight, H = height, sCr = serum creatinine level, V = total kidney volume). The MDRD and CKD-EPI had relatively better accuracy than the other creatinine-based methods (30.7% vs. 32.3% within 10% and 78.0% vs. 73.0% within 30%, respectively). However, the new-vGFR formula had the most accurate results among all of the analyzed methods (37.4% within 10% and 84.6% within 30%).

CONCLUSIONS

The new-vGFR can replace dGFR or creatinine-based GFR for assessing kidney function in donors and healthy individuals.

KEY POINTS

• Accurate prediction of GFR is crucial in kidney donors. • DTPA is accurate but costly, invasive, and clinically difficult to apply. • Volume-based GFR estimation performs as well as the Cr-based method. • New volume-based GFR estimation performs better among GFR estimation formulas.

Clinical Decision Making in a Patient with Stage 5 CKD--Is eGFR Good Enough?

The development and widespread use of serum creatinine concentration-based prediction equations to calculate eGFR have been major advances for detection of patients with CKD and the epidemiologic study of CKD and its outcomes. However, these equations as well as those that also incorporate serum cystatin C concentration provide GFR estimates that, although reasonably precise on average, can differ markedly and in clinically important ways from actual GFR. Thus, it is important that clinicians who use these equations for clinical decision-making be familiar with their strengths and weaknesses and have an appreciation of their potential for error. More precise knowledge of actual GFR is important in certain clinical circumstances, including, as presented in this Attending Rounds, patients with stage 5 CKD, in whom decisions regarding dialysis initiation are necessary. Nephrologists should have the ability to accurately determine GFR when needed if clinical circumstances suggest inaccuracy of the calculated eGFR reported by the clinical laboratory.

Biomarkers in chronic kidney disease, from kidney function to kidney damage

Chronic kidney disease (CKD) typically evolves over many years, with a long latent period when the disease is clinically silent and therefore diagnosis, evaluation and treatment is based mainly on biomarkers that assess kidney function. Glomerular filtration rate (GFR) remains the ideal marker of kidney function. Unfortunately measuring GFR is time consuming and therefore GFR is usually estimated from equations that take into account endogenous filtration markers like serum creatinine (SCr) and cystatin C (CysC). Other biomarkers such as albuminuria may precede kidney function decline and have demonstrated to have strong associations with disease progression and outcomes. New potential biomarkers have arisen with the promise of detecting kidney damage prior to the currently used markers. The aim of this review is to discuss the utility of the GFR estimating equations and biomarkers in CKD and the different clinical settings where these should be applied. The CKD-Epidemiology Collaboration equation performs better than the modification of diet in renal disease equation, especially at GFR above 60 mL/min per 1.73 m². Equations combining CysC and SCr perform better than the equations using either CysC or SCr alone and are recommended in situations where CKD needs to be confirmed. Combining creatinine, CysC and urine albumin to creatinine ratio improves risk stratification for kidney disease progression and mortality. Kidney injury molecule and neutrophil gelatinase-associated lipocalin are considered reasonable biomarkers in urine and plasma to determine severity and prognosis of CKD.

Autofluorescence of Skin Advanced Glycation End Products: Marker of Metabolic Memory in Elderly Population

BACKGROUND

Advanced glycation end products are involved in the vascular complications of diabetes, in chronic kidney disease, and in the aging process. Their accumulation in the elderly people, as reflected by skin autofluorescence (sAF), may be a marker of metabolic memory. We aimed to examine the association of sAF with glycemic and renal status 10 years earlier in older persons.

METHODS

In retrospective cohort study, 328 elderly community dwellers aged of 75 years and over had sAF measurement 10 years after their inclusion in the Three-City cohort. Fasting plasma glucose and serum creatinine were measured at baseline and at 10-year follow-up. In 125 participants, HbA1c was available at these two times. Associations between sAF and the glycemic and renal status 10 years before were analyzed by multivariate linear regression adjusted for age, sex, hypertension, body mass index, hypertriglyceridemia, and smoking.

RESULTS

Participants were 82.4 (standard deviation = 4.1) years on average, and their mean sAF was 2.8 (standard deviation = 0.7) arbitrary units (AU). After adjustment, sAF was higher in participants with long-standing diabetes (+0.38 AU, p = .01) or chronic kidney disease (+0.29 AU, p = .02) compared with healthy participants. sAF was related to fasting plasma glucose (+1 mmol/L associated with +0.08 AU, p = .01) and HbA1c (+1% associated with +0.15 AU, p = .03) 10 years earlier, but not to the current fasting plasma glucose (p = .82) and HbA1c (p = .32). sAF was also related to the distal and current estimated glomerular filtration rates (p = .002 and .004, respectively).

CONCLUSIONS

sAF reflects glycemic and renal status 10 years before, supporting its value as a marker of metabolic memory in the elderly people.

Genome-wide association study reveals a polymorphism in the podocyte receptor RANK for the decline of renal function in coronary patients

Impaired kidney function is a significant health problem and a major concern in clinical routine and is routinely determined by decreased glomerular filtration rate (GFR). In contrast to single assessment of a patients' kidney function providing only limited information on patients' health, serial measurements of GFR clearly improves the validity of diagnosis. The decline of kidney function has recently been reported to be predictive for mortality and vascular events in coronary patients. However, it has not been investigated for genetic association in GWA studies. This study investigates for the first time the association of cardiometabolic polymorphisms with the decline of estimated GFR during a 4 year follow up in 583 coronary patients, using the Cardio-Metabo Chip. We revealed a suggestive association with 3 polymorphisms, surpassing genome-wide significance (p = 4.0 e-7). The top hit rs17069906 (p = 5.6 e-10) is located within the genomic region of RANK, recently demonstrated to be an important player in the adaptive recovery response in podocytes and suggested as a promising therapeutic target in glomerular diseases.

The relationship between estimated GFR based on the CKD-EPI formula and renal inulin clearance in potential kidney donors

It is not yet clear whether or not renal function in the living donor can be sufficiently assessed by estimated glomerular filtration rate (GFR) using creatinine-based equations. The present paper investigates the relationship between GFR values determined using renal inulin clearance (Cin) and those estimated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula. Our study was performed in 287 potential kidney donors with a mean age of 48 ± 10 years. Mean Cin was 1.47 ± 0.28 (1.10 - 2.50) mL/s/1.73 m2. Total bias when using the CKDEPI formula was -0.0183 mL/s/1.73 m2, precision 0.263 mL/s/1.73 m2, and accuracy 90.6% within ± 30% of Cin. The sensitivity of CKD-EPI to estimate a decrease in Cin below 1.33 mL/s/1.73 m2 was 50.5%, with an 85% specificity of detecting a value above the cutoff. Receiver-operating curve analysis for the above produced an area under the curve of 0.766 ± 0.0285 (CI 0.712 - 0.813). For donor screening purposes, CKD-EPI should be interpreted with great caution.

Low-level cadmium exposure and effects on kidney function

OBJECTIVES

The nephrotoxicity of cadmium at low levels of exposure, measured by urinary cadmium, has recently been questioned since co-excretion of cadmium and proteins may have causes other than cadmium toxicity. The aim of this study was to explore the relation between kidney function and low or moderate cadmium levels, measured directly in kidney biopsies.

METHODS

We analysed cadmium in kidney biopsies (K-Cd), blood (B-Cd) and urine (U-Cd) from 109 living kidney donors in a cross-sectional study. We measured glomerular filtration rate (GFR), cystatin C in serum, albumin, β-2-microglobulin (B2M), retinol-binding protein (RBP), α-1-microglobulin (A1M), N-acetyl-β-d-glucosaminidase and kidney injury molecule 1 (KIM-1) in 24 h and overnight urine.

RESULTS

We found significant positive associations between A1M excretion and K-Cd in multiple regression models including age, sex, weight, smoking and urinary flow rate. This association was also present in never-smokers. A1M was also positively associated with B-Cd and U-Cd. GFR and the other biomarkers of kidney function were not associated with K-Cd. GFR estimated from serum cystatin C showed a very poor correlation with measured GFR. KIM-1, RBP and possibly albumin were positively associated with U-Cd, but only in overnight urine. No associations were found with B2M.

CONCLUSIONS

Our results suggest that A1M in urine is a sensitive biomarker for effects of low-level cadmium exposure. A few associations between other renal biomarkers and U-Cd, but not K-Cd, were probably caused by physiological co-excretion or chance.

Cadmium, type 2 diabetes, and kidney damage in a cohort of middle-aged women

BACKGROUND

It has been proposed that diabetic patients are more sensitive to the nephrotoxicity of cadmium (Cd) compared to non-diabetics, but few studies have examined this in humans, and results are inconsistent.

AIM

To test the hypothesis that women with type 2 diabetes mellitus (DM) or impaired glucose tolerance (IGT) have higher risk of kidney damage from cadmium compared to women with normal glucose tolerance (NGT).

METHODS

All 64-year-old women in Gothenburg, Sweden, were invited to a screening examination including repeated oral glucose tolerance tests. Random samples of women with DM, IGT, and NGT were recruited for further clinical examinations. Serum creatinine was measured and used to calculate estimated glomerular filtration rate (eGFR). Albumin (Alb) and retinol-binding protein (RBP) were analyzed in a 12h urine sample. Cadmium in blood (B-Cd) and urine (U-Cd) was determined using inductively coupled plasma mass spectrometry. Associations between markers of kidney function (eGFR, Alb, and RBP) and quartiles of B-Cd and U-Cd were evaluated in models, including also blood pressure and smoking habits.

RESULTS

The mean B-Cd (n=590) was 0.53 µg/L (median 0.34 µg/L). In multivariable models, a significant interaction was seen between high B-Cd (upper quartile, >0.56 µg/L) and DM (point estimate +0.40 mg Alb/12h, P=0.04). In stratified analyzes, the effect of high B-Cd on Alb excretion was significant in women with DM (53% higher Alb/12h, P=0.03), but not in women with IGT or NGT. Models with urinary albumin adjusted for creatinine showed similar results. In women with DM, the multivariable odds ratio (OR) for microalbuminuria (>15 mg/12h) was increased in the highest quartile of B-Cd vs. B-Cd quartiles 1-3 in women with DM (OR 4.2, 95% confidence interval 1.1-12). No such effect was found in women with IGT or NGT. There were no associations between B-Cd and eGFR or excretion of RBP, and no differences between women with DM, IGT, or NGT regarding effect of B-Cd on eGFR or RBP.

CONCLUSION

The present study provides support for the hypothesis that women with DM have higher risk of renal glomerular damage from cadmium exposure compared to women without DM.

The consequences of chronic kidney disease mislabeling in living kidney donors

Despite numerous studies that substantiate its long-term safety, barriers to kidney donation persist. These include issues of insurability after donation and its consequent financial and emotional burdens. We present 2 cases in which mislabeling of kidney donors as having chronic kidney disease shortly after kidney donation adversely affected their insurability. A concerted effort should be made to affect public policy such that insurability and the psychosocial well-being of living donors are protected.

Neutrophil gelatinase-associated lipocalin and cystatin C for the prediction of clinical events in patients with advanced heart failure and after ventricular assist device placement

BACKGROUND

Progressive renal dysfunction develops in patients with advanced HF. We evaluated neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C compared with established markers of renal function in patients with heart failure (HF) because they might improve prognostic assessment of patients with HF.

METHODS

Serum samples were collected from 40 patients with stable HF (age: 58 ± 8 years, body mass index [BMI]: 28.4 ± 6.4 kg/m(2)), 40 HF patients undergoing ventricular assist device (VAD) implantation (age: 53 ± 11 years, BMI: 26.8 ± 5.5 kg/m(2)), 40 patients undergoing VAD removal at cardiac transplantation, and 24 controls (age: 48 ± 7 years, BMI: 29.4 ± 4.2 kg/m(2)). Clinical data were collected from institutional medical records. NGAL and cystatin C levels were measured by enzyme-linked immunosorbent assay and estimated glomerular filtration rate (eGFR) calculated using the Modification of Diet in Renal Disease formula.

RESULTS

Patients with stable HF showed elevated NGAL and cystatin C levels compared with controls (NGAL: 114.9 ± 48.3 ng/mL vs 72.0 ± 36.6 ng/mL, p < 0.0001; cystatin C: 1490.4 ± 576.1 ng/mL vs 954.7 ± 414.2 ng/mL, p = 0.0026). Unlike cystatin C, NGAL increased in advanced HF patients requiring VAD implantation (158.7 ± 74.8 ng/mL, p < 0.001). On VAD support, NGAL levels decreased (127.1 ± 80.4 ng/mL, p = 0.034). NGAL was higher in patients who developed right ventricular failure (187.8 ± 66.0 vs 130.9 ± 67.0 ng/mL, p = 0.03) and irreversible renal dysfunction (190.0 ± 73.8 ng/mL vs 133.8 ± 54.2 ng/mL, p < 0.05), whereas cystatin C, creatinine, and eGFR were not different. NGAL correlated with eGFR (r = -0.2188, p = 0.01).

CONCLUSIONS

NGAL levels correlate with HF severity and hemodynamic improvement after VAD placement. Our findings suggest a role of this novel biomarker as a marker of severity and prognosis in patients with HF.

Performance of creatinine-based GFR estimating equations in solid-organ transplant recipients

BACKGROUND

Accurate assessment of kidney function is important for the management of solid-organ transplant recipients. In other clinical populations, glomerular filtration rate (GFR) most commonly is estimated using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine or the 4-variable MDRD (Modification of Diet in Renal Disease) Study equation. The accuracy of these equations compared with other GFR estimating equations in transplant recipients has not been carefully studied.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

Solid-organ transplant recipients longer than 6 months posttransplantation from 5 clinical populations (N=3,622, including recipients of kidney [53%], liver [35%], and other or multiple organs [12%]).

INDEX TEST

Estimated GFR (eGFR) using creatinine-based GFR estimating equations identified from a systematic review of the literature. Performance of the CKD-EPI creatinine and the MDRD Study equations was compared with alternative equations.

REFERENCE TEST

Measured GFR (mGFR) from urinary clearance of iothalamate or plasma clearance of iohexol.

MEASUREMENTS

Error (difference between mGFR and eGFR) expressed as P30 (proportion of absolute percent error <30%) and mean absolute error.

RESULTS

We identified 26 GFR estimating equations. Mean mGFR was 55.1±22.7 (SD) mL/min/1.73 m(2). P30 and mean absolute error for the CKD-EPI and the MDRD Study equations were 78.9% (99.6% CI, 76.9%-80.8%) for both and 10.6 (99.6% CI, 10.1-11.1) versus 11.0 (99.6% CI, 10.5-11.5) mL/min/1.73 m(2), respectively; these equations were more accurate than any of the alternative equations (P <0.001 for all pairwise comparisons for both measures). They performed better than or as well as the alternative equations in most subgroups defined by demographic and clinical characteristics, including type of transplanted organ.

LIMITATIONS

Study population included few nonwhites and people with solid-organ transplants other than liver and kidneys.

CONCLUSIONS

The CKD-EPI creatinine and the MDRD Study equations perform better than the alternative creatinine-based estimating equations in solid-organ transplant recipients. They can be used for clinical management.

Non-renal effects and the risk assessment of environmental cadmium exposure

BACKGROUND

Exposure to cadmium (Cd) has long been recognized as a health hazard, both in industry and in general populations with high exposure. Under the currently prevailing health risk assessment, the relationship between urinary Cd (U-Cd) concentrations and tubular proteinuria is used. However, doubts have recently been raised regarding the justification of basing the risk assessment on this relationship at very low exposure.

OBJECTIVES

Our objective was to review available information on health effects of Cd exposure with respect to human health risk assessment.

DISCUSSION

The associations between U-Cd and urinary proteins at very low exposure may not be due to Cd toxicity, and the clinical significance of slight proteinuria may also be limited. More importantly, other effects have been reported at very low Cd exposure. There is reason to challenge the basis of the existing health risk assessment for Cd. Our review of the literature found that exposure to low concentrations of Cd is associated with effects on bone, including increased risk of osteoporosis and fractures, and that this observation has implications for the health risk assessment of Cd. Other effects associated with Cd should also be considered, in particular cancer, although the information is still too limited for appropriate use in quantitative risk assessment.

CONCLUSION

Non-renal effects should be considered critical effects in the health risk assessment of Cd.

Aging and chronic kidney disease

A recent report has dealt with geriatric nephrology, including epidemiology and pathophysiology of chronic kidney disease (CKD), attempting to get nephrologists to pay more attention to elderly CKD patients. The aims of this article are to summarize the morphological and functional properties of the aging kidney, and to better understand nephrology care for elderly CKD patients. The kidneys are affected by the aging process, which results in numerous effects on the renal system. In addition, the elderly population is hetereogenous - some have a decline in GFR explained by diseases that complicate aging such as arteriosclerosis with hypertension, whereas in the most of healthy adults the decline in GFR is much more modest and not inevitable. The values for normal estimated glomerular filtration rate (eGFR) in aging population have important implications for the diagnosis of CKD in the elderly. However, the MDRD equation underestimates mean eGFR by 25% and the CKD-EPI equation underestimates mean GFR by 16%. This bias may lead to misclassifying healthy older persons as having CKD. It is also still unknown whether and how age influences the predictive role of other risk factors for end-stage renal disease (ESRD) and death in referred as well as unreferred patients. The risk of ESRD was reported to be higher than the risk of death without ESRD for ages <60 years, and independent of eGFR. Proteinuria significantly increased the risk of ESRD with advancing age. In older patients on nephrology care, the risk of ESRD prevailed over mortality even when eGFR was not severely impaired. Proteinuria increases the risk of ESRD, while the predictive role of other modifiable risk factors was unchanged compared with younger patients. The decision to initiate renal replacement therapy in the elderly is complicated by more challenges than in younger patients. Calorie restriction and Klotho deficiency may be a candidate therapeutic target for attenuating kidney aging. © 2014 S. Karger AG, Basel.

Estimation of glomerular filtration rate from serum creatinine and cystatin C in octogenarians and nonagenarians

BACKGROUND

Equations to estimate GFR have not been well validated in the elderly and may misclassify persons with chronic kidney disease (CKD). We measured GFR and compared the performance of the Modification of Diet in Renal Disease (MDRD), the Chronic Kidney Disease-Epidemiology Collaboration (CKD-Epi) and the Berlin Initiative Study (BIS) equations based on creatinine and/or cystatin C in octogenarians and nonagenarians.

METHODS

Using cross-sectional analysis we assessed 95 very elderly persons (mean 85 years) living in the community. GFR was measured by iohexol (mGFR) and compared with estimates using six equations: MDRD, CKD-Epi_creatinine, CKD-Epi_cystatin, CKD-Epi_creatinine-cystatin, BIS_creatinine and BIS_creatinine-cystatin.

RESULTS

Mean mGFR was 55 (range,19-86) ml/min/1.73 m(2). Bias was smaller with the CKD-Epi_creatinine-cystatin and the CKD-Epi_creatinine equations (-4.0 and 1.7 ml/min/1.73 m(2)). Accuracy (percentage of estimates within 30% of mGFR) was greater with the CKD-Epi_creatinine-cystatin, BIS_creatinine-cystatin and BIS_creatinine equations (85%, 83% and 80%, respectively). Among the creatinine-based equations, the BIS_creatinine had the greatest accuracy at mGFR < 60 ml/min/1.73 m(2) and the CKD-Epi_creatinine was superior at higher GFRs (79% and 90%, respectively). The CKD-Epi_creatinine-cystatin, BIS_creatinine-cystatin and CKD-Epi_cystatin equations yielded the greatest areas under the receiver operating characteristic curve at GFR threshold = 60 ml/min/1.73 m 2 (0.88, 0.88 and 0.87, respectively). In participants classified based on the BIS_creatinine, CKD-Epi_cystatin, or BIS_creatinine-cystatin equations, the CKD-Epi_creatinine-cystatin equation tended to improve CKD classification (net reclassification index: 12.7%, p = 0.18; 6.7%, p = 0.38; and 15.9%; p = 0.08, respectively).

CONCLUSIONS

GFR-estimating equations CKD-Epi_creatinine-cystatin and BIS_creatinine-cystatin showed better accuracy than other equations using creatinine or cystatin C alone in very elderly persons. The CKD-Epi_creatinine-cystatin equation appears to be advantageous in CKD classification. If cystatin C is not available, both the BIS_cr equation and the CKD-Epi_cr equation could be used, although at mGFR < 60 ml/min/1.73 m(2), the BIS_cr equation seems to be the best alternative.