CORRELATION OF PLASMA-CONCENTRATIONS OF CYSTATIN-C AND CREATININE TO INULIN-CLEARANCE IN A PEDIATRIC POPULATION

Measurement of blood concentrations of cystatin C (cysC), a cysteine p rotease inhibitor present in human plasma, has been suggested for use as an indicator of glomerular filtration rate (GFR) in a manner analog ous to the use of plasma creatinine (SCR). In this study, cysC and SCR were measured in plasma from pediatric patients (4-19 years) with ren al disease for whom a ''gold standard'' measurement of GFR via inulin clearance (C-IN) was available. The data analyses were divided into tw o age groups: group A (4-12 years, n = 26) and group B (12-19 years, n = 34). For both age groups, the linear correlation coefficient of [cy sC](-1) vs C-IN (mL/min/1.73 m(2)) (r = 0.765 for group A and r = 0.86 9 for group B) was less than that of the linear correlation coefficien t of [SCR](-1) vs C-IN (r = 0.841 for group A and r = 0.892 for group B). As a single measurement for detection of abnormal GFR, however, th e optimum receiver-operator characteristic point for cysC measurement (for group A at cysC >1.2 mg/L, sensitivity = 80%, specificity = 91%; and for group B at cysC >1.4 mg/L, sensitivity = 87%, specificity = 10 0%) was numerically superior to that for SCR measurement (for group A at SCR >8.0 mg/L, sensitivity = 67%, specificity = 100%; and for group B at SCR >9.0 mg/L, sensitivity = 91%, specificity = 91%), using a re ference value for normal GFR of C,, > 90 mL/min/1.73 m(2). However, th ese differences were not statistically significant. CysC measurement a ppears to be broadly equivalent to SCR measurement for estimation of G FR in pediatric patients.