Estimation of glomerular filtration rate by MDRD equation in athletes: role of body surface area

Creatinine-based equations to estimate the glomerular filtration rate (GFR) have recently been advocated over serum creatinine values as a valuable tool to more accurately assess kidney function. The Cockcroft–Gault (CG) equation requires a body weight parameter, whereas the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease (MDRD) Study equations do not. In this study we evaluated the effect of the calculated body surface area (BSA) on MDRD values in professional athletes characterized from different body mass index, gender, and sport discipline. Serum creatinine concentration was measured by Jaffe reaction in 17 male rugby players and 28 male and 26 female swimmers, before the start of training and throughout the competitive season. The values of estimated GFR (eGFR) calculated for creatinine determination by means of CG and CDK-EPI with respect to MDRD formula showed a significant difference in different groups of athletes. The statistical significance was confirmed for BSA-corrected MDRD-derived eGFR values in rugby players and in male swimmers, but not in female swimmers, who showed a BSA close to the “standard” value of 1.73 m² traditionally included in MDRD equation. The CG equation can overestimate the eGFR in healthy overweight subjects such as rugby players, whereas the MDRD formula systematically underestimates it. The differences between the two equations increase as a function of BMI, appearing highest in rugby players and lowest in female swimmers. Real BSA correction of the MDRD equation could help to avoid an overestimation of renal excretory function in subjects with increased BSA.