CYSTATIN-C - A NEW MARKER OF GLOMERULAR-FILTRATION RATE IN CHILDREN INDEPENDENT OF AGE AND HEIGHT

Objectives. Serum creatinine is the most common endogenous marker of r enal function. The proportionality between creatinine production and m uscle mass requires adjustment for height and body composition. The lo w molecular weight protein cystatin C is produced by all nucleated cel ls and eliminated by glomerular filtration. Therefore, cystatin C was studied as an alternative marker of glomerular filtration rate (GFR) i n children. Methods. Cystatin C and creatinine were measured in sera f rom inulin clearance (C-In) examinations performed in 184 children age d 0.24 to 17.96 years. C-In ranged from 7 to 209 mL/min/1.73 m(2) (med ian, 77). Results. The reciprocal of cystatin C correlated better with C-In (r = 0.88) than the reciprocal of creatinine (r = 0.72). Stepwis e regression analysis identified no covariates for the correlation bet ween cystatin C and C-In, whereas height was a covariate for creatinin e. Using an estimate of GFR from serum creatinine and height, correlat ion with C-In was similar to cystatin C, but female gender and dystrop hy were associated with an overestimation of GFR. Diagnostic accuracy in the identification of reduced GFR measured as area under the receiv er-operating characteristic plot was 0.970 +/- 0.135 (mean +/- SE) for cystatin C and 0.894 +/- 0.131 for creatinine (NS). A cutoff cystatin C concentration of 1.39 mg/L had 90% sensitivity and 86% specificity for detecting abnormal GFR. Conclusion. Unlike creatinine, serum cysta tin C reflects renal function in children independent of age, gender, height, and body composition.