Detecting reduced renal function in children: comparison of GFR-models and serum markers.

BACKGROUND: The aim of this study was to compare the ability of renal indicators [serum creatinine (SCr), cystatin C (SCysC)] and glomerular filtration rate (GFR)-models to discriminate normal and reduced renal function. As a single cut-off level will always lead to false classifications, we propose using two cut-off levels, dividing renal function into normal or reduced, with an intermediate "gray zone" of indeterminable results. METHODS: Glomerular filtration rate was measured by plasma clearance of (51)Cr-EDTA (13.7-147.4 mL/min/1.73 m(2)) in 119 children (age range 2.3-14.9 years). Reduced renal function was defined as a GFR of <82 mL/min/1.73 m(2). SCr, SCysC, age-normalized creatinine (SCr-ratio), and eight published GFR-models were compared for their ability to correctly classify renal function as normal or reduced. Cut-off levels were determined so as to give 99 % certainty outside the gray zone. RESULTS: The multivariable GFR-models by Schwartz et al. (J Am Soc Nephrol 2009; 20:629-637) and Zappitelli et al. (Am J Kidney Dis 2006; 48:221-230) and two models by Andersen et al. [Am J Kidney Dis 2012; 59(1):50-57: body cell mass (BCM)-model and Weight-model] performed significantly better than all other variables (P < 0.01), with the BCM-model performing the best (P < 0.05). The SCr-based Schwartz formula and SCr-ratio both performed better than SCr and SCysC. CONCLUSIONS: Among the 119 children enrolled in this study and the renal indicators tested, the BCM-model had the best diagnostic performance in terms of screening for normal or reduced renal function, and the SCr-ratio was a superior diagnostic tool to both SCr and SCysC.

GFR prediction from cystatin C and creatinine in children: effect of including body cell mass.

BACKGROUND: Aiming to develop a more accurate cystatin C-based model for estimation of glomerular filtration rate (GFR) in children, we hypothesized that inclusion of body cell mass (BCM) would increase the accuracy of the GFR estimate in comparison to a well-established GFR reference method. STUDY DESIGN: Diagnostic test accuracy study. SETTINGS & PARTICIPANTS: 119 children (mean age, 8.8; range, 2.3-14.9 years) referred for GFR measurement by chromium 51 ethylenediaminetetraacetic acid ((51)Cr-EDTA) clearance (mean GFR, 98; range, 13.7-147.4 mL/min/1.73 m(2)). INDEX TEST: GFR estimations by the 2 prediction models resulting from theoretical considerations corroborated by forward stepwise variable selection: GFR (mL/min) = 0.542 × (BCM/SCysC)(0.40) × (height × BSA/SCr)(0.65) and GFR (mL/min) = 0.426 × (weight/SCysC)(0.39) × (height × BSA/SCr)(0.64), where SCysC is serum cystatin C level, BSA is body surface area, and SCr is serum creatinine level. The accuracy and precision of these models were compared with 7 previously published prediction models using random subsampling cross-validation. Local constants and coefficients were calculated for all models. Root mean square error, R(2), and percentage of predictions within ±10% and ±30% of the reference GFR were calculated for all models. Based on 1,000 runs of the cross-validation procedure, median values and 2.5th and 97.5th quantiles of the validation parameters were calculated. REFERENCE TEST: GFR measurement by (51)Cr-EDTA clearance. RESULTS: The BCM model predicted 98% within ±30% of reference GFR and 66% within ±10%, which was higher than for any other model. The weight model predicted 97.5% within ±30% of reference GFR and 62% within ±10%. The BCM model had the highest R(2) and the smallest root mean square error. LIMITATIONS: Included only 9 children with GFR <60 mL/min/1.73 m(2). Lack of independent validation cohort. CONCLUSIONS: The novel BCM model predicts GFR with higher accuracy than previously published models. The weight model is almost as accurate as the BCM model and allows for GFR estimation without knowledge of BCM. However, endogenous methods are still not sufficiently accurate to replace exogenous markers when GFR must be determined with high accuracy.

Comparison of within- and between-subject variation of serum cystatin C and serum creatinine in children aged 2-13 years.

BACKGROUND: Previously, data on both the within-subject (SD(I)) and the between-subject (SD(G)) variation of cystatin C in children has not been reported. Thus, this study aimed to determine this biological variation including analytical variation (SD(A)) of both cystatin C and creatinine to characterize the two analytes as renal function markers in children. METHODS: On two consecutive days blood samples for duplicate analysis of cystatin C (nephelometric, Dade Behring) and creatinine (enzymatic, Roche) were obtained from 30 children (11 females and 19 males, mean age 8.3 range 2-13 years) referred for GFR measurements by (51)Cr-EDTA clearance. For determination of the between-subject variation only children with normal GFR (n=21) were included. Data were adjusted for the well known age-related increase in creatinine. RESULTS: The results are given as coefficients of variation. The within-subject variations were identical for both analytes (6.4%). The between-subject variation was 11.1% for cystatin C and 28.4% for creatinine, though decreasing to 20.1% after adjusting for age. The analytical variation was 1.7% and 2.5% for cystatin C and creatinine, respectively. The index of individuality (IOI = SD(I)/SD(G)) was 0.65 for cystatin C and 0.25 for creatinine, though increasing to 0.36 after age-adjustment. CONCLUSION: The within-subject variation was identical and low for cystatin C and creatinine suggesting that the two are equally suitable for serial monitoring of renal function in children. Based on the low IOI neither analyte, however, seems suitable as a screening marker of renal function in a healthy population of children using population-based reference intervals.

Measuring glomerular filtration rate in children; can cystatin C replace established methods? A review.

Our aim was to evaluate published methods that use serum cystatin C (s-CysC) for measuring glomerular filtration rate (GFR) in children and to discuss advantages and limitations of s-CysC and of established GFR methods. A comprehensive literature review of clinical studies in children evaluating s-CysC or CysC-based formulas and plasma creatinine or creatinine-based formulas against an exogenous reference method using receiver operating characteristics (ROC) curves or Bland-Altman plots is presented. The comparison of s-CysC with plasma creatinine indicated that s-CysC was superior to plasma creatinine in five of 13 studies; four studies showed no difference, and, in four studies, no statistical comparison was made. Comparison of s-CysC and the Schwartz formula showed that s-CysC was superior to the Schwartz formula in two of seven studies; two studies demonstrated no difference, and, in one study, the Schwartz formula was superior to s-CysC. In two studies no statistical comparison was made. The CysC-based prediction equations all had high accuracy but low agreement when compared with a reference GFR, in the range of 30-40% at best. S-CysC is most likely superior to plasma creatinine and at least equal to creatinine-based formulas. CysC-based prediction equations are at least as good as creatinine-based formulas but cannot replace exogenous methods.