Abstract
Background. Previously, data on both the within-subject (SDI) and the between-subject (SDG) variation of cystatin C in children has not been reported. Thus, this study aimed to determine this biological variation including analytical variation (SDA) 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 51Cr-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 = SDI/SDG) 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.
Published Version
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