Simple cystatin C-based prediction equations for glomerular filtration rate compared with the modification of diet in renal disease prediction equation for adults and the Schwartz and the Counahan-Barratt prediction equations for children

Background: Serum creatinine is the most commonly used marker for estimation of glomerular filtration rate (GFR). To compensate for its drawbacks as a GFR marker, several prediction equations including several parameters are being used, with the Modification of Diet in Renal Disease (MDRD), Schwartz, and Counahan-Barratt equations being the ones most widely accepted for estimation of relative GFR in mL (.) min(-1) (.) (1.73 m(2))(-1). The present study analyzes whether these GFR prediction equations for adults and children might be replaced by simple prediction equations based on plasma concentrations of cystatin C. Methods: Data from 536 patients (0.3-93 years), consecutively referred for determination of GFR by an invasive gold standard procedure, were used for the analysis. Calculations of bias (median percentage of error), correlation (adjusted R-2), and percentage of estimates within 30% and 50% of measured GFR were used in the comparisons. Results: A cystatin C-based prediction equation using only concentration in mg/L and a prepubertal factor: GFR [mL (.) min(-1) (.) (1.73 m(2))(-1)] = 84.69 x cystatin C (mg/L)(-1.680) x 1.384 (if a child < 14 years) assessed GFR equally well or better than the simplified MDRD, the Schwartz, and the Counahan-Barratt prediction equations for the adult ( :18 years) and juvenile groups of the investigated cohort. Age did not influence the cystatin C-based prediction equation for adults, whereas gender did, but with a factor close to unity (0.948 for females). Conclusion: A GFR prediction equation based solely on cystatin C (in mg/L) and a prepubertal factor might replace the simplified MDRD prediction equation for adults and the Schwartz and Counahan-Barratt prediction equations for children. (c) 2005 American Association for Clinical Chemistry.