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The Values of Estimated Glomerular Filtration Rate Calculated with Creatinine and Cystatin C Based Equations in Healthy Adults by Marijana Dajak, Svetlana Ignjatović, Snežana Jovičić, Nada Markić-Singh

The glomerular filtration rate (GFR) is widely accepted as the best overall index of kidney function. GFR can be measured as the clearance of exogenous or endogenous filtration markers or clinically estimated from serum concentrations of creatinine or cystatin C. Recently, it has been recommended that an estimated GFR (eGFR) should be reported in addition to the value of filtration markers. In this study, we determined the values of eGFR, based on creatinine and cystatin C equations, in 125 healthy volunteers aged 20-75 years. Creatinine was measured by a kinetic alkaline picrate method on an ARCHITECT ci8200 analyzer (Abbott Diagnostics, Wiesbaden, Germany). Cystatin C was determined by a latex particle-enhanced immunonephelometric assay (BNII, Dade Behring, Marburg, Germany). The eGFR values were calculated for creatinine using the Modification of Diet in Renal Disease (MDRD) study equation and Rule´s quadratic equation and for cystatin C according to the equation published by Hoek et al. The reference intervals for eGFRs with MDRD, Rule´s quadratic and Hoek´s equations were calculated nonparametrically and were determined to be 63.5-124.6 mL/min/1.73 m^2, 78.3-139.2 mL/min/1.73 m^2 and 72.2-115.6 mL/min/1.73 m^2, respectively. According to the US National Kidney Foundation, chronic kidney disease (CKD) can be defined as a GFR < 60 mL/min/1.73 m^2. Our results showed that healthy adults had eGFR values > 63.5 mL/min/1.73 m^2. However, it is important to note that these normal values overlap with values in stages 1 and 2 of CKD, thus an eGFR greater than 60 mL/min/1.73 m^2 does not exclude kidney disease.

DOI: Clin. Lab. 2008;54:153-159