RESUMO
BACKGROUND: Cystatin C (cysC) is said to be an ideal marker for glomerular filtration rate (GFR), independent of external factors such as age, nutrition and inflammation. The authors compared the accuracy and precision of cysC-based and creatinine (Cr)-based GFR estimates using Cr51-EDTA GFR method as a reference. METHODS: Serum concentrations of cysC and Cr were measured in adults over 17 yr (n=170) and children below 17 yr (n=79) who had had GFR estimated by Cr51-EDTA method. CysC-based GFR was estimated by the formula of Thierry [CysC-based GFR estimates (mL/min/1.73 m2)=78 x (1/cysC, in mg/L)+4] and Cr-based GFR by the formula of modified Modification of Diet in Renal Disease [MDRD II, Cr-based GFR estimates (mL/min/1.73 m2)=186 x (Scr)(-1.154) x (Age)(-0.203) x 0.742 (for a female patient) x 1.212 (for a black patient). RESULTS: In comparison with Cr51-EDTA GFR, in children below 17 yr, the bias +/- standard deviation (SD) of cysC-based and Cr-based GFR estimates were 7.5 +/- 6.1 and 106.5 +/- 98.2, respectively, in the range of below 90 of Cr51-EDTA GFR (mL/min/1.73 m2), and 33.7 +/- 33.0 and 174.4 +/- 18.8 in the range of over 90. In adults over 17 yr, the respective figures were 13.1 +/- 11.0 and 17.4 +/- 29.8 in below 90, and 21.2 +/- 20.1 and 83.6 +/- 108.8 in over 90 of Cr51-EDTA GFR. CONCLUSIONS: CysC-based GFR estimates show acceptable ranges of biases over the whole age and GFR ranges. CysC-based GFR estimates is considered to be the marker for GFR, which could be used without limitation of age and GFR ranges.