INTRODUCTION: Determination of the glomerular filtration rate (GFR) is critical for the selection of a potential living kidney donor. Since July 2008 our center has been using plasma clearance of 51Cr-EDTA (51Cr-EDTA-Cl) to evaluate GFR of the donors. This decision was taken after the validation with the renal inulin clearance, the gold-standard for GFR measurement. Modification of diet in renal disease (MDRD) formula is known to be inadequate for living donor selection, underestimating GFR and leading to inappropriate exclusion of the donors. The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula could be an alternative for estimation of the donor GFR. We compared the calculated GFR by MDRD and CKD-EPI formulas with the measured 51Cr-EDTA-Cl of living donors in our center.

METHODS: We evaluated 431 living kidney donors who donated kidneys between July 2008 and September 2014. 51Cr-EDTA-Cl was done with a single dose infusion and two blood-time samples (4 and 6 hours). Cutoff for donation was 51Cr-EDTA-Cl above 80/ml/min per 1.73m2. Comparison of 51Cr-EDTA-Cl with the estimated GFR (eGFR) by MDRD and CKD-EPI equations was done using Spearman correlation and Bland and Altman (BA) statistical analysis.

RESULTS: There was a predominance of female donors (n=269, 62%) with a mean age of 40±9 years. The median of the measured GFR by 51Cr-EDTA-Cl was 106 ml/min per 1.73m2 (min 76, max 160) and by eGFR MDRD and CKD-EPI was 95 (min 64, max 171) and 101 (min 67, max 137) ml/min/1.73m2, respectively. Compared to 51Cr-EDTA-Cl, the CKD-EPI had a lower mean of the differences (bias) than MDRD equation (4,91 vs 8,75 ml/min/1.73m2) but only mild difference in the precision, with the standard deviation of the differences of 15 ml/min for CKD-EPI and 16ml/min for MDRD. Gender differences were not observed. Underestimation of GFR 51Cr-EDTA-Cl below 80ml/min was higher in MDRD equation, occurring in 6% of the donors when MDRD was applied and in 3% with CKD-EPI equation (p<0,05). These donors would be inappropriated excluded.

CONCLUSION: The CKD-EPI equation has a higher performance in the GFR estimation of living donors compared to MDRD. eGFR greater than 110 ml/min by CKD-EPI equation and greater than 112 ml/min by MDRD equation seems to be suitable for donation. Caution is still required for evaluation of true GFR in lower eGFRs. Therefore, the widespread use of eGFR for donor selection cannot be recommended.

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