BACKGROUND In living kidney donations the accuracy of renal function is fundamental, especially for potential donors who have limited renal function (creatinine clearance levels [CCr] <90 mL/m/1.73 m(2)), are >50 years old, and who have cardiovascular risk factors that might favor the development of kidney diseases. OBJECTIVE To compare the direct measured glomerular filtration (mGFR) using 51Cr-EDTA and the estimations based on creatinine (estimated glomerular filtration rate [eGFR]): CCr with 24-hour urine, and estimated using Cockroft-Gault (adjusted using body surface area, Mosteller formula), modification of diet in renal disease-4 (MDRD-4), MDRD-6, and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) to determine the usefulness of different methods to evaluate the kidney function. METHODS The kidney function evaluation was performed for 37 potential kidney donors using the 51Cr-EDTA method. The GFR obtained through the 51Cr-EDTA was compared with the CCr values in 24-hour urine and eGFR based on creatinine (Cockcroft-Gault, MDRD-4, MDRD-6, and CKD-EPI). RESULTS Using the Bland Altman graph, the most dispersed results were obtained with the eGFR using CCr in 24-hour urine and CKD-EPI. By means of Passing and Bablok, MDRD-4 and MDRD-6 showed the highest approximation to the reference method proposed to be substituted, whereas CCr showed a high dispersion. CONCLUSIONS The eGFR using MDRD-4 and MDRD-6 formulas revealed the best adjustment to the measure by 51Cr-EDTA. This might represent the best option if a direct eGFR measure is not available.