Is serum cystatin C the marker of choice to predict glomerular filtration rate in paediatric patients?

Background It has been suggested that serum cystatin C (cyst-C) concentration provides a better indication of changes in glomerular filtration rate (GFR) than does serum creatinine concentration. Methods Because of conflicting results as to the usefulness of cyst-C, we compared the GFRs calculated from serum cyst-C, inulin clearance and endogenous creatinine clearance in children. GFRs calculated from cystatin concentration, inulin clearance following a single injection and endogenous creatinine clearance using Jaffe and enzymic methods were compared in 66 children (1.3-21.9 years) with a variety of renal disorders. Receiver operating curve analysis was used to determine the cut-off value that would give the best discrimination between normal and decreased GFR. Results The serum cyst-C concentration ranged from 0.66 to 7.61 mg/L (median 1.94). Serum creatinine Jaffe concentration (creat-J) ranged from 38 to 871 mumol/L (median 105) and creatinine enzymatic concentration (creat-E) ranged from 28 to 862 mumol/L (median 126). The linear correlation coefficient (R) of 1/cyst-C versus GFR (R= 0.937) did not differ from either that of 1/creat-J versus GFR (R= 0.918) or that of 1/creat-E versus GFR (R = 0.901). These coefficients had overlapping confidence intervals. The areas under the curve for cyst-C, creat-J and creat-E were 0.967, 0.977 and 0.924, respectively, and were not significantly different from each other. For cyst-C, the optimal cut-off was 1.1 mg/L. Conclusions Serum cyst-C is equivalent to creat-J and creat-E as a marker for estimating the GFR in the paediatric population studied.