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

Abstract

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 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 = 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.

Key Words::

• Glomerular filtration rate
• kidney diseases
• kidney function tests
• renal insufficiency

Acknowledgments

Support for this study was provided by Aarhus University Hospital, The John and Birthe Meyer Foundation, The Aase and Ejnar Danielsen Foundation, The Heinrich Kopps Foundation, The Danish National Research Council and The University of Aarhus.

We thank all the technicians at Aalborg and Skejby Hospital for their help in this project and Mrs Lena T. Pedersen for excellent technical assistance.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.