Objective: To evaluate relations among different equations for GFR calculation based on serum concentrations of cystatin C or creatinine and other analytes. Design: Retrospective analysis of data from routine examination of kidney function in outpatients and hospitalized patients. Material and Methods: Selection of 533 examination of kidney function from laboratory information system, calculation of glomerular filtration rate (GFR) according to MDRD formula (GFR MDRD) and with three equations based on serum cystatin C levels (GFR cystatin). Results: Interquartile range for serum creatinine was 82–171 µmol/l, for cystatin C 1.04–2.46 mg/l, values of GFR were normal and decreased. GFR MDRD displayed differences between men and women, values in men were higher of about 0.2 ml/s (P = 0.0005). Coefficient of correlation (r) between GFR MDRD and GFR cystatin was 0.892, higher correlation was found in women (r = 0.933), weak correlation was connected with cystatin C under 1.5 mg/l (r = 0.538). Values of GFR MDRD were of about 0.15 ml/s higher than values of GFR cystatin. Conclusions: Estimates of GFR according MDRD formula and cystatin C are not interchangeable. GFR MDRD displayed significant differences between sexes. Correlation among methods is lower with increased GFR. MDRD formula overestimated results with increased serum concentrations of cystatin C, there are differences among different equations derived from serum cystatin C.

        Key words: cystatin C, glomerular filtration rate, MDRD formula.