New standardized cystatin C and creatinine GFR equations in children validated with inulin clearance

This study compares glomerular filtration rate (GFR) equations in children based on standardized cystatin C (CYSC) and creatinine (CREA) and their combinations with renal clearance of inulin (C-inulin). A total of 220 children with different renal disorders were referred for C-inulin (median 84 ml/min/1.73 m(2)). Bias, precision (interquartile range, IQR), and accuracy (percentage of estimates +/- 30 % of C-inulin; P30) were evaluated for two cystatin C equations, CAPA(CYSC) and Berg(CYSC), for creatinine equations, Schwartz(CREA) and Gao(CREA), the arithmetic mean of CAPA(CYSC) and Schwartz(CREA) (MEAN(CAPA+Schwartz)), Berg(CYSC) and Schwartz(CREA) (MEAN(BERG+SCHWARTZ)) and the composite equation Chehade(CYSC+CREA). Overall results of CAPA(CYSC), Berg(CYSC), Schwartz(CREA), Gao(CREA), MEAN(CAPA+Schwartz,) MEAN(BERG+SCHWARTZ) and Chehade(CYSC+CREA) were: median bias -7.6/-4.9/-3.7/-2.3/-4.6/-4.0/-10.1 %, IQR 20.0/19.9/21.7/22.4/21.0/20.9/23.3 ml/min/1.73 m(2) and P30 86/86/80/83/89/91/83 %. The cystatin C equations, MEAN(CAPA+Schwartz) and MEAN(BERG+SCHWARTZ) had a more stable performance across subgroups compared with Schwartz(CREA), Gao(CREA) and Chehade(CYSC+CREA). Cystatin C was the preferred filtration marker for GFR estimation in children, while the benefit of combining cystatin C and creatinine deserves further investigations.