Appraisal of GFR-Estimating Equations Following Kidney Donation

Background: It is not clear which serum creatinine-based glomerular filtration rate (GFR)-estimating model performs best in kidney donors. Study Design: Study of diagnostic accuracy. Setting & Participants: From a population of 3,698 kidney donors, 255 donors underwent iohexol GFR measurement (mGFR). Index Test (Intervention): mGFR by means of plasma disappearance of iohexol. Reference Test or Outcome: GFR was estimated (eGFR) by using the Cockcroft-Gault equation (eGFR_CG), Mayo Clinic equation (eGFR_MC), and Modification of Diet in Renal Disease (MDRD) Study equation (eGFR_MDRD). Results: Mean mGFR was 71.8 ± 11.8 mL/min/1.73 m², and 85.5% had mGFR greater than 60 mL/min/1.73 m². eGFR_CG underestimated mGFR by 3.96 ± 13.3 mL/min/1.73 m² and was within 30% of mGFR 89.4% of the time. eGFR_MC overestimated mGFR by 8.44 ± 11.9 mL/min/1.73 m² and was within 30% of mGFR in 83.1% of cases. eGFR_MDRD underestimated mGFR by only 0.43 ± 11.7 mL/min/1.73 m², and the proportion within 30% of mGFR was greatest in the tested model; 94.1% of the time. However, eGFR_MC was most accurate in classifying donors according to having eGFR less than 60 mL/min/1.73 m². Limitations: Lack of ethnic diversity and response bias. Conclusions: The MDRD Study equation is least biased, and because it is routinely reported by most laboratories, it is the best readily available model for estimating GFR in kidney donors.