Estimating glomerular filtration rates by use of both cystatin C and standardized serum creatinine avoids ethnicity coefficients in Asian patients with chronic kidney disease

Optimal Glomerular Filtration Rate Equations for Various Age Groups, Disease Conditions and Ethnicities in Asia: A Systematic Review

(1) Background: The performance of estimated glomerular filtration rate (eGFR) equations in the Asian population has been widely questioned. The primary objective of this study was to gather evidence regarding optimal GFR equations in Asia for various age groups, disease conditions, and ethnicities. The secondary objective was to see whether the equations based on the combination of creatinine and cystatin C biomarkers if employed are satisfactory across different age groups and disease conditions in various ethnicities in Asia compared to those based on either of the single biomarkers. (2) Methods: Validation studies that had both creatinine and cystatin C-based equations either alone or in combination, validated in specific disease conditions, and those which compared the performance of these equations with exogenous markers were eligible only. The bias, precision, and 30% accuracy (P30) of each equation were recorded accordingly. (3) Results: Twenty-one studies consisting of 11,371 participants were included and 54 equations were extracted. The bias, precision, and P30 accuracies of the equations ranged from -14.54 to 9.96 mL/min/1.73 m2, 1.61 to 59.85 mL/min/1.73 m2, and 4.7% to 96.10%. The highest values of P30 accuracies were found for the JSN-CKDI equation (96.10%) in Chinese adult renal transplant recipients, for the BIS-2 equation (94.5%) in Chinese elderly CKD patients, and Filler equation (93.70%) also in Chinese adult renal transplant recipients. (4) Conclusions: Optimal equations were identified accordingly and it was proven that combination biomarker equations are more precise and accurate in most of the age groups and disease conditions. These can be considered equations of choice for the specific age groups, disease conditions, and ethnicities within Asia.

Diagnostic Accuracy of Serum Cystatin C for Early Recognition of Nephropathy in Type 2 Diabetes Mellitus

Objectives

Diabetic nephropathy is one of the major complications that develop over time in type 2 diabetes mellitus (T2DM). This prospective study was conducted to assess the diagnostic accuracy of serum cystatin C in detecting diabetic nephropathy at earlier stages.

Materials and Methods

This study was undertaken on 50 cases of T2DM and 50 healthy subjects as controls. Demographic and anthropometric data and blood and urine samples were collected. The concentration of serum cystatin C (index test) and traditional markers of diabetic nephropathy, serum creatinine, and urinary microalbumin (the reference standard) were estimated. Similarly, blood glucose, glycated haemoglobin (HbA1c), triglycerides, total cholesterol, high-density lipoprotein (HDL) cholesterol, and urinary creatine were measured.

Results

The mean ± SD serum cystatin C was significantly higher in T2DM as compared to control (1.07 ± 0.38 and 0.86 ± 0.12 mg/dl, respectively, p < 0.001). The mean ± SD bodyweight, BMI, W : H ratio, pulse, SBP, and DBP were 66.4 ± 12.6 kg, 26.2 ± 5.6 kg/m², 1.03 ± 0.09, 78 ± 7, 125 ± 16 mm of Hg, and 77 ± 9 mm of Hg, respectively, in cases. A significant difference in HDL cholesterol (p=0.018) and serum cystatin C (p < 0.001) was observed among different grades of nephropathy. Cystatin C had a significant positive correlation with age (r = 0.323, p=0.022), duration of T2DM (r = 0.326, p=0.021), and UACR (r = 0.528, p < 0.001) and a significant negative correlation with eGFR CKD-EPI cystatin C (r = −0.925, p < 0.001). The area under ROC curve for serum cystatin C (0.611, 95% CI: 0.450–0.772) was greater than for serum creatinine (0.429, 95% CI: 0.265–0.593) though nonsignificant.

Conclusion

Serum cystatin C concentration increases with the progression of nephropathy and duration of diabetes in Nepalese T2DM patients suggesting cystatin C as a potential marker of renal impairment in T2DM patients.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Impact of Kidney Function on Cardiovascular Risk and Mortality: A Comparison of South Asian and European Cohorts

BACKGROUND

Evidence is limited on ethnic differences in associations between kidney function markers and mortality or cardiovascular disease (CVD).

METHODS

Baseline cross-sectional analysis and longitudinal follow-up study of a UK population-based cohort of 1,116 Europeans and 1,104 South Asians of predominantly Indian descent, age 52 ± 7 years at baseline (1988-1991). Kidney function was estimated using Cystatin C and creatinine-based chronic kidney disease (CKD) Epidemiology Collaboration estimated glomerular filtration rate (eGFR) equations, and urinary albumin-creatinine ratio (ACR). Mortality was captured at 27 years, and incident CVD at 22 years, from death certification, medical records and participant report. Longitudinal associations between eGFR/ACR and mortality/incident CVD were examined using Cox models.

RESULTS

eGFRcys was lower and ACR higher in South Asians than Europeans. eGFRcys and -eGFRcreat were more strongly associated with outcomes in Europeans than South Asians. Conversely, associations between ACR and outcomes were greater in South Asians than Europeans, for example, for CVD mortality: HRs (95% CI) adjusted for CVD risk factors and ACR/eGFRcys as appropriate, p for ethnicity interaction: eGFRcys: Europeans: 0.76 (0.62-0.92), South Asians: 0.92 (0.78-1.07), p = 0.05, eGFRcreat: Europeans 0.81 (0.67-0.99), South Asians 1.18 (0.97-1.41), p = 0.002, ACR: -Europeans: 1.24 (1.08-1.42), South Asians: 1.39 (1.25-1.57), p= 0.23. Addition of all CKD measures to a standard CVD risk factor model modestly improved prediction capability in -Europeans; in South Asians only ACR contributed to improvement.

CONCLUSIONS

Strong associations between ACR and outcomes in South Asians of predominantly Indian origin, and null associations for eGFRcys and eGFRcreat, suggest that ACR may have greater utility in CVD risk prediction in South Asians. Further work is needed to validate these -findings.

Non-GFR Determinants of Low-Molecular-Weight Serum Protein Filtration Markers in the Elderly: AGES-Kidney and MESA-Kidney

BACKGROUND

Studies in chronic kidney disease populations suggest that the non-glomerular filtration rate (GFR) determinants of serum levels of the low-molecular-weight protein filtration markers cystatin C, β2-microglobulin (B2M), and beta-trace protein (BTP) are less affected by age, sex, and ethnicity than those of creatinine.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

Predominantly elderly participants selected from the Age, Gene/Environment Susceptibility Kidney Study (AGES-Kidney; N=683; mean [SD] age, 79 [4] years; GFR, 62 [17]mL/min/1.73 m2) and from the Multi-Ethnic Study of Atherosclerosis Kidney Study (MESA-Kidney; N=273; mean [SD] age, 70.5 [9] years; GFR, 73 [19]mL/min/1.73 m2).

PREDICTORS

Demographic and clinical factors hypothesized to be associated with conditions affecting non-GFR determinants of the filtration markers.

OUTCOMES

Measured GFRs and estimated GFRs (eGFRs) based on creatinine, cystatin C, B2M, and BTP levels (eGFRcr, eGFRcys, eGFRB2M, and eGFRBTP, respectively). Residual associations of factors with eGFR after accounting for measured GFR as the parameter of interest.

RESULTS

eGFRcys, eGFRB2M, and eGFRBTP had significantly less strong residual associations with age and sex than eGFRcr in both AGES-Kidney and MESA-Kidney and were not associated with ethnicity (black vs white) in MESA-Kidney. After adjusting for age, sex, and ethnicity, residual associations with most clinical factors were smaller than observed with age and sex. eGFRcys and eGFRB2M, but not eGFRBTP, had significant residual associations with C-reactive protein levels in both studies.

LIMITATIONS

Small sample size may limit power to detect associations. Participants may be healthier than the general population.

CONCLUSIONS

Similar to previous studies in chronic kidney disease, in community-dwelling elders, cystatin C, B2M, and BTP levels are less affected than creatinine level by age and sex and are not affected by ethnicity. Both cystatin C and B2M levels may be affected by inflammation. These findings are important for the development and use of GFR estimating equations based on low-molecular-weight serum proteins throughout the range in GFRs.

Non-GFR Determinants of Low-Molecular-Weight Serum Protein Filtration Markers in CKD

BACKGROUND

Unlike the case with creatinine, conditions affecting the non-glomerular filtration rate (GFR) determinants of low-molecular-weight serum proteins, β-trace protein (BTP), β2-microglobulin (B2M), and cystatin C, are not well characterized.

STUDY DESIGN

Pooled cross-sectional analysis of 3 studies.

SETTING & PARTICIPANTS

3,156 persons with chronic kidney disease from the MDRD (Modification of Diet in Renal Disease) Study, AASK (African American Study of Kidney Disease and Hypertension), and CRIC (Chronic Renal Insufficiency Cohort) Study.

PREDICTORS

Demographic and clinical factors hypothesized to be associated with non-GFR determinants of the filtration markers, selected from literature review and physiologic and clinical considerations.

OUTCOMES

Serum creatinine, BTP, B2M, and cystatin C levels.

RESULTS

In multivariable-adjusted errors-in-variables regression models that included adjustment for measured GFR (mGFR) and mGFR measurement error, creatinine level had stronger associations with male sex, black race, and higher urine creatinine excretion than the other filtration markers. BTP was associated less strongly with age, similar in direction with sex, and opposite in direction with race than creatinine level. Like cystatin C, B2M level was associated less strongly with age, sex, and race than creatinine level. BTP, B2M, and cystatin C levels were associated more strongly than creatinine level with other factors, including urine protein excretion and weight for BTP, smoking and urine protein excretion for B2M, and smoking for cystatin C.

LIMITATIONS

Findings may not be generalizable to populations without chronic kidney disease, and residual confounding with GFR due to incomplete adjustment for GFR measurement error.

CONCLUSIONS

Like creatinine, serum levels of low-molecular-weight proteins are affected by conditions other than GFR. Knowledge of these conditions can aid the interpretation of GFR estimates and risk using these markers and guide the use of these filtration markers in developing GFR estimating equations.

Comparison of creatinine and cystatin C based eGFR in the estimation of glomerular filtration rate in Indigenous Australians: The eGFR Study

BACKGROUND

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation that combines creatinine and cystatin C is superior to equations that include either measure alone in estimating glomerular filtration rate (GFR). However, whether cystatin C can provide any additional benefits in estimating GFR for Indigenous Australians, a population at high risk of end-stage kidney disease (ESKD) is unknown.

METHODS

Using a cross-sectional analysis from the eGFR Study of 654 Indigenous Australians at high risk of ESKD, eGFR was calculated using the CKD-EPI equations for serum creatinine (eGFRcr), cystatin C (eGFRcysC) and combined creatinine and cystatin C (eGFRcysC+cr). Reference GFR (mGFR) was determined using a non-isotopic iohexol plasma disappearance technique over 4h. Performance of each equation to mGFR was assessed by calculating bias, % bias, precision and accuracy for the total population, and according to age, sex, kidney disease, diabetes, obesity and c-reactive protein.

RESULTS

Data were available for 542 participants (38% men, mean [sd] age 45 [14] years). Bias was significantly greater for eGFRcysC (15.0mL/min/1.73m²; 95% CI 13.3-16.4, p<0.001) and eGFRcysC+cr (10.3; 8.8-11.5, p<0.001) compared to eGFRcr (5.4; 3.0-7.2). Accuracy was lower for eGFRcysC (80.3%; 76.7-83.5, p<0.001) but not for eGFRcysC+cr (91.9; 89.3-94.0, p=0.29) compared to eGFRcr (90.0; 87.2-92.4). Precision was comparable for all equations. The performance of eGFRcysC deteriorated across increasing levels of c-reactive protein.

CONCLUSION

Cystatin C based eGFR equations may not perform well in populations with high levels of chronic inflammation. CKD-EPI eGFR based on serum creatinine remains the preferred equation in Indigenous Australians.

Performance of the CKD-EPI creatinine-cystatin C glomerular filtration rate estimation equations in a multiethnic Asian population

INTRODUCTION

Clinical practice guidelines recommend using creatinine-based equations to estimate glomerular filtration rates (GFRs). While these equations were formulated for Caucasian-American populations and have adjustment coefficients for African-American populations, they are not validated for other ethnicities. The Chronic Kidney Disease-Epidemiology Collaborative Group (CKD-EPI) recently developed a new equation that uses both creatinine and cystatin C. We aimed to assess the accuracy of this equation in estimating the GFRs of participants (healthy and with chronic kidney disease [CKD]) from a multiethnic Asian population.

METHODS

Serum samples from the Asian Kidney Disease Study and the Singapore Kidney Function Study were used. GFR was measured using plasma clearance of 99mTc-DTPA. GFR was estimated using the CKD-EPI equations. The performance of GFR estimation equations were examined using median and interquartile range values, and the percentage difference from the measured GFR.

RESULTS

The study comprised 335 participants (69.3% with CKD; 38.5% Chinese, 29.6% Malays, 23.6% Indians, 8.3% others), with a mean age of 53.5 ± 15.1 years. Mean standardised serum creatinine was 127 ± 86 μmol/L, while mean standardised serum cystatin C and mean measured GFR were 1.43 ± 0.74 mg/L and 67 ± 33 mL/min/1.73 m2, respectively. The creatinine-cystatin C CKD-EPI equation performed the best, with an estimated GFR of 67 ± 35 mL/min/1.73 m2.

CONCLUSION

The new creatinine-cystatin C equation estimated GFR with little bias, and had increased precision and accuracy in our multiethnic Asian population. This two-biomarker equation may increase the accuracy of population studies on CKD, without the need to consider ethnicity.

Aortic stiffness and kidney disease in an elderly population

BACKGROUND/AIMS

The causes of chronic kidney disease (CKD) in older people are not well understood. Aortic stiffness increases with age and results in the transmission of increased pulsatility into the kidney microvasculature, potentially contributing to CKD in older populations.

METHODS

We utilized data from the Age, Gene/Environment, Susceptibility-Reykjavik Study, a community-based prospective cohort study of cardiovascular disease (CVD) in Iceland. The relationship of carotid pulse pressure (CPP) and carotid-femoral pulse wave velocity (CFPWV) with estimated glomerular filtration rate (eGFR) based on creatinine and cystatin C and urine albumin-creatinine ratio (ACR) was assessed using linear regression, adjusting for demographics and CVD risk factors.

RESULTS

940 participants (mean (SD) age 75.8 (4.7) years, mean (SD) CFPWV 12.9 (4.2) m/s, mean (SD) CPP 69 (21) mm Hg, mean (SD) eGFR 68 (16) ml/min/1.73 m(2), and median (IQR) ACR 3 (2-6) mg/g) were included in this study. At CPP greater than 85 mm Hg, a higher CPP was associated with a lower eGFR in unadjusted analyses but not after adjustment. CPP was significantly associated with a higher ACR in fully adjusted models (β (95% CI) = 0.14 (0.03, 0.24) ln mg/g per SD). Higher CFPWV was associated with lower eGFR and higher ACR in unadjusted analyses but not after adjustment.

CONCLUSION

Greater aortic stiffness may be associated with modestly higher levels of albuminuria in the elderly. The association between aortic stiffness and lower eGFR may be confounded by age and CVD risk factors.

A comparison of the effects of ketamine and remifentanil on renal functions in coronary artery bypass graft surgery

We have investigated the effects of ketamine-based and remifentanil-based anesthetic protocol on perioperative serum cystatin-C levels, and creatinine and/or cystatin-C-based eGFR equations in terms of acute kidney injury in coronary artery bypass graft (CABG) surgery. Using a simple randomization method (coin tossing), patients were divided into the two groups and not-blinded to the anesthetist. Remifentanil-midazolam-propofol or ketamine-midazolam-propofol-based anesthetic regimen was chosen. Different eGFR formulas using creatinine (MDRD, CKD-EPI, Cockrauft Gault); cystatin-C (eGFR1, eGFR2) or a combination of creatinine and cystatin-C (eGFR 3) were used to calculate estimated glomerular filtration rates (eGFRs). High-sensitive troponin T was used to determine if ketamine use in coronary surgery contributed to myocardial cell damage. Thirty-seven patients were included in the study (remifentanil group = 19, ketamine Group = 18). Urea, creatinine, cystatin-C levels were comparable between the groups in all the measurement times and also postoperative day 2 samples showed statistically higher results compared to baseline (p < 0.001). Effects of ketamine and remifentanil on renal functions were found similar. Creatinine and cystatin-C-based eGFR equations resulted similar in our study. Reversible stage 1 acute kidney injury (AKI) was observed on postoperative day 2 in seven patients from the remifentanil group and six patients from the ketamine group. Hs-troponin T was found to be higher in postoperative day 1 samples; there were no significant difference between the groups. Our results indicated that patients who have normal renal functions undergoing on-pump coronary bypass surgery, effects of ketamine and remifentanil on renal functions in terms of AKI were found to be similar.

Chronic kidney disease screening methods and its implication for Malaysia: an in depth review

Chronic Kidney Disease has become a public health problem, imposing heath, social and human cost on societies worldwide. Chronic Kidney Disease remains asymptomatic till late stage when intervention cannot stop the progression of the disease. Therefore, there is an urgent need to detect the disease early. Despite the high prevalence of Chronic Kidney Disease in Malaysia, screening is still lacking behind. This review discusses the strengths and limitations of current screening methods for Chronic Kidney Disease from a Malaysian point of view. Diabetic Kidney Disease was chosen as focal point as Diabetes is the leading cause of Chronic Kidney Disease in Malaysia. Screening for Chronic Kidney Disease in Malaysia includes a urine test for albuminuria and a blood test for serum creatinine. Recent literature indicates that albuminuria is not always present in Diabetic Kidney Disease patients and serum creatinine is only raised after substantial kidney damage has occurred.  Recently, cystatin C was proposed as a potential marker for kidney disease but this has not been studied thoroughly in Malaysia.  Glomerular Filtration Rate is the best method for measuring kidney function and is widely estimated using the Modification of Diet for Renal Disease equation. Another equation, the Chronic Kidney Disease Epidemiology Collaboration Creatinine equation was introduced in 2009. The new equation retained the precision and accuracy of the Modification of Diet for Renal Disease equation at GFR < 60ml/min/1.73m2, showed less bias and improved precision at GFR>60ml/min/1.73m2. In Asian countries, adding an ethnic coefficient to the equation enhanced its performance. In Malaysia, a multi-ethnic Asian population, the Chronic Kidney Disease Epidemiology Collaboration equation should be validated and the Glomerular Filtration Rate should be reported whenever serum creatinine is ordered. Reporting estimated Glomerular Filtration Rate will help diagnose patients who would have been otherwise missed if only albuminuria and serum creatinine are measured.

Comparing GFR Estimating Equations Using Cystatin C and Creatinine in Elderly Individuals

Current guidelines recommend reporting eGFR using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations unless other equations are more accurate, and recommend the combination of creatinine and cystatin C (eGFRcr-cys) as more accurate than either eGFRcr or eGFRcys alone. However, preferred equations and filtration markers in elderly individuals are debated. In 805 adults enrolled in the community-based Age, Gene/Environment Susceptibility (AGES)-Reykjavik Study, we measured GFR (mGFR) using plasma clearance of iohexol, standardized creatinine and cystatin C, and eGFR using the CKD-EPI, Japanese, Berlin Initiative Study (BIS), and Caucasian and Asian pediatric and adult subjects (CAPA) equations. We evaluated equation performance using bias, precision, and two measures of accuracy. We first compared the Japanese, BIS, and CAPA equations with the CKD-EPI equations to determine the preferred equations, and then compared eGFRcr and eGFRcys with eGFRcr-cys using the preferred equations. Mean (SD) age was 80.3 (4.0) years. Median (25th, 75th) mGFR was 64 (52, 73) ml/min per 1.73 m(2), and the prevalence of decreased GFR was 39% (95% confidence interval, 35.8 to 42.5). Among 24 comparisons with the other equations, CKD-EPI equations performed better in 9, similar in 13, and worse in 2. Using the CKD-EPI equations, eGFRcr-cys performed better than eGFRcr in four metrics, better than eGFRcys in two metrics, and similar to eGFRcys in two metrics. In conclusion, neither the Japanese, BIS, nor CAPA equations were superior to the CKD-EPI equations in this cohort of community-dwelling elderly individuals. Using the CKD-EPI equations, eGFRcr-cys performed better than eGFRcr or eGFRcys.

Call for the use of a common equation for glomerular filtration rate estimation in East and South-East Asia

BACKGROUND

Estimated glomerular filtration rate (eGFR) is currently calculated using various equations and serum creatinine (Scr) value measured by different assays. Differences among these eGFRs deserve further study.

METHODS

Volunteers from eight Asian regions (n=3283; age 20-65 years, 1454 men, 1829 women) were recruited. The Chronic Kidney Disease Epidemiology Collaboration equation (EPI), Modification of Diet in Renal Disease Study equation (MDRD) for Japanese (MDRDJap) and MDRD for Chinese (MDRDChi) were selected. Jaffe and enzymatic assays were used to measure Scr. Six eGFRs were obtained for each volunteer: EPI equation using Scr value of enzymatic assay (EPI/E) and Jaffe assay (EPI/J); MDRDJap equation using Scr value of the two assays (MDRDJap/E, MDRDJap/J); and MDRDChi equation using Scr value of the two assays (MDRDChi/E, MDRDChi/J).

RESULTS

Neither Scr nor eGFR showed significant regional difference. We compared eGFR calculated using the same equation but with different assays. The medians (2.5%, 97.5%) of eGFR difference were 2.0 (-7, 14) mL/min/1.73 m(2) for EPI, 3.0 (-12.0, 18.0) mL/min/1.73 m(2) for MDRDJap, and 5.0 (-18, 30) mL/min/1.73 m(2) for MDRDChi. We also compared eGFR calculated using different equations but with the same assay. The medians (2.5%, 97.5%) of eGFR difference were 11 (-6, 56) mL/min/1.73 m(2) between MDRDChi/E and EPI/E; 26 (9, 35) mL/min/1.73 m(2) between EPI/E and MDRDJap/E; and 39 (22, 65) mL/min/1.73 m(2) between MDRDChi/E and MDRDJap/E, respectively.

CONCLUSIONS

eGFR difference caused by using different equations is much larger than that caused by using different Scr assays. A common equation for GFR estimation is encouraged for use in Asians.

Comparison of CKD-EPI Cystatin C and Creatinine Glomerular Filtration Rate Estimation Equations in Asian Indians

Background. Chronic kidney disease (CKD) is identified in the general population using estimated glomerular filtration rates (eGFR) calculated from a serum creatinine-based equation, the chronic kidney disease-epidemiology collaboration (CKD-EPI) equation. Using serum cystatin C in combination may improve eGFR accuracy. We evaluated the new CKD-EPI equations incorporating cystatin C in a population of Asian Indians in classifying CKD across body mass index, diabetes, and hypertension status. Methods. We retrieved standardized serum creatinine and serum cystatin C data from a cohort of 2877 Asian Indians aged 40–80 years from the Singapore Indian Eye Study and calculated eGFR (in mL/min/1.73 m²) with the new CKD-EPI equations and serum creatinine only equation. Results. The creatinine only equation mean eGFR (88 ± 17) was similar to using spline Log cystatin C (88 ± 22). The lowest mean eGFR (81 ± 21) was obtained with the spline Log cystatin C—age, sex, and weight equation. The creatinine only equation had the fewest participants (7.1%) with eGFR <60 and spline Log cystatin C—age, sex, and weight equation had the most (16.1%). Conclusions. Using serum cystatin C resulted in widely varying eGFR which significantly affected the classification of chronic kidney disease.

Comparison of CKD-EPI Cystatin C and Creatinine Glomerular Filtration Rate Estimation Equations in Asian Indians

Background. Chronic kidney disease (CKD) is identified in the general population using estimated glomerular filtration rates (eGFR) calculated from a serum creatinine-based equation, the chronic kidney disease-epidemiology collaboration (CKD-EPI) equation. Using serum cystatin C in combination may improve eGFR accuracy. We evaluated the new CKD-EPI equations incorporating cystatin C in a population of Asian Indians in classifying CKD across body mass index, diabetes, and hypertension status. Methods. We retrieved standardized serum creatinine and serum cystatin C data from a cohort of 2877 Asian Indians aged 40-80 years from the Singapore Indian Eye Study and calculated eGFR (in mL/min/1.73 m(2)) with the new CKD-EPI equations and serum creatinine only equation. Results. The creatinine only equation mean eGFR (88 ± 17) was similar to using spline Log cystatin C (88 ± 22). The lowest mean eGFR (81 ± 21) was obtained with the spline Log cystatin C-age, sex, and weight equation. The creatinine only equation had the fewest participants (7.1%) with eGFR <60 and spline Log cystatin C-age, sex, and weight equation had the most (16.1%). Conclusions. Using serum cystatin C resulted in widely varying eGFR which significantly affected the classification of chronic kidney disease.

Body mass index and preclinical kidney disease in Indian adults aged 40 years and above without chronic kidney disease

BACKGROUND

Obesity is associated with diabetes and hypertension, two major risk factors for chronic kidney disease (CKD). Recently, it has been shown that obesity is associated with preclinical kidney disease defined by elevated levels of cystatin C among those without CKD in US adults. However, the association of obesity with cystatin C is not known in industrialized Asian populations.

METHODS

We examined 2,052 Indian adults aged 40-80 years in Singapore who were free of CKD defined as a serum creatinine-based estimated glomerular filtration rate (eGFRcr) <60 mL/min/1.73 m(2) and/or the presence of microalbuminuria. Body mass index (BMI) values were categorized into normal (18.5-24.9), overweight (25-29.9) and obese (≥30 kg/m(2)). Elevated serum cystatin C was defined as cystatin C ≥1 mg/L.

RESULTS

Overweight and obesity were significantly associated with elevated levels of cystatin C after adjusting for potential confounders including diabetes and hypertension and eGFRcr. Compared to those with normal weight, the odds ratio (95 % confidence interval) of elevated cystatin C was 1.49 (1.17-1.88) for overweight and 3.20 (2.33-4.39) for obese. This association was consistently present when BMI was analyzed as a continuous variable and also in subgroups of men, women and in those without diabetes mellitus or hypertension.

CONCLUSIONS

Higher BMI levels are associated with preclinical kidney disease in Indian adults aged 40 years and above without CKD.

The impact of chronic kidney disease and cardiovascular comorbidity on mortality in a multiethnic population: a retrospective cohort study

OBJECTIVE

To assess the impact of chronic kidney disease (CKD) and cardiovascular comorbidity on mortality in a multiethnic primary care population.

DESIGN

Retrospective cohort study.

SETTING

Inner-city primary care trust in West Midlands, UK.

PARTICIPANTS

Individuals aged 40 years and older, of South Asian, black or white ethnicity, registered with a general practice and with their kidney function checked within the last 12 months (n=31 254).

OUTCOME MEASURE

All-cause mortality.

RESULTS

Reduced estimated glomerular filtration rate, higher albuminuria, older age, white ethnicity (vs South Asian or black ethnicity) and increasing cardiovascular comorbidities were independent determinants of a higher mortality risk. In the multivariate model including comorbidities and kidney function, the HR for mortality for South Asians was 0.697 (95% CI 0.56 to 0.868, p=0.001) and for blacks it was 0.533 (95% CI 0.403 to 0.704, p<0.001) compared to whites.

CONCLUSIONS

The HR for death is lower for South Asian and black individuals compared to white individuals. This is, in part, independent of age, gender, socioeconomic status, kidney function and comorbidities. Risk of death is higher in individuals with CKD and with a higher cumulative cardiovascular comorbidity.

Relationship between serum cystatin C and creatinine or dialysis adequacy in patients on chronic maintenance hemodialysis

Background

Glomerular filtration rate (GFR) is widely estimated by serum creatinine based equations such as Cockcroft-Gault (CG) standardized for body surface, and an abbreviated formula derived from MDRD (modification of diet in renal disease) study. However, some studies suggested that creatinine based estimation of GFR formula can be replaced by cystatin C based formula.

Objectives

The aim of this study was to determine whether cystatin C based equation could be used as an indicator for renal function in hemodialysis patients compared to MDRD equation; and whether cystatin C, a dialyzable molecule, was related to Kt/V, the marker for dialysis adequacy.

Patients and Methods

In this cross-sectional study, 98 patients on chronic hemodialysis were included. Plasma levels of urea and creatinine were measured before and after dialysis, and cystatin C was measured before dialysis. GFR was calculated and compared.

Results

The mean age of patients was 55.50 ± 16.10 (24-86) years and 66 cases were male (67.3%). The GFR was estimated at 6.05 ± 2.36 and 5.83 ± 2.19 cc/min by MDRD and cystatin C based formulas, respectively, with a significant correlation (r = 0.51; P < 0.001). Serum cystatin C level was 9.74 ± 2.47 mg/L which showed significant reverse correlation with both MDRD (r = -0.46; P < 0.001) and cystatin C based formulas (r = -0.87; P < 0.001). Neither creatinine nor serum cystatin C showed correlation with Kt/V, as the marker of dialysis adequacy.

Conclusions

Serum cystatin C may be considered as an indicator of renal function in patients under maintenance hemodialysis.

Demystifying ethnic/sex differences in kidney function: is the difference in (estimating) glomerular filtration rate or in serum creatinine concentration?

BACKGROUND

The recent evaluation of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for estimating the glomerular filtration rate (GFR) in multiple ethnicities has raised the question on how well this equation performs for African-American and Asian subjects. There is no doubt that serum creatinine (Scr) concentration differs between ethnicities and sexes. We show that creatinine-based equations for white populations may be inaccurate for estimating GFR in other ethnic/gender groups, especially in populations from Asia.

METHODS

This study presents a mathematical analysis of the CKD-EPI-equation complemented with a literature review of median and reference values for IDMS-standardized Scr-concentrations for multiple ethnicities.

RESULTS

The study shows that at equal eGFR-CKD-EPI-values, the ratio of Scr between females and males equals 0.79 and between other ethnicities/sexes and white males is constant too. From this information, it is possible to calculate mean Scr-values that correspond very well with literature values directly obtained from Scr-distributions in healthy white males and females and in black males, but the discrepancy is larger for other populations.

CONCLUSIONS

Our results confirm the criticism that has been raised for using the CKD-EPI-equation for these ethnicities. An alternative eGFR-model is proposed based on a population-normalized Scr that needs further validation.