Measured and estimated GFR in healthy potential kidney donors

BACKGROUND: Nonradiolabeled iothalamate clearance is an accurate way to determine glomerular filtration rate (GFR). Objectives of this study are to define the normal range of nonradiolabeled iothalamate clearance in potential kidney donors and assess whether creatinine-based GFR estimates are accurate in this population. METHODS: Medical records of 365 potential kidney donors were reviewed. GFR was measured using clearance of nonradiolabeled iothalamate. Linear regression analysis was used to determine age- and sex-specific normal range values for GFR and serum creatinine. The abbreviated Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault prediction equations were used to estimate GFR from serum creatinine levels. RESULTS: GFR declined significantly with increasing age (P < 0.001) and was lower in women than men (P < 0.001). Men at the age of 20 years had an estimated mean GFR of 129 mL/min that declined by 4.6 mL/min/decade. Women at the age of 20 years had a mean GFR of 123 mL/min that declined by 7.1 mL/min/decade. Regression analysis of GFR normalized to body surface area (nGFR) was significant for age (P < 0.001), but not sex (P = 0.826). A 20-year-old had a mean nGFR of 111 mL/min/1.73 m2 that declined by 4.9 mL/min/1.73 m2/decade. Correlation between measured nGFR and estimated GFR was weak (r = 0.26 for abbreviated MDRD equation; r = 0.35 for Cockcroft-Gault equation). CONCLUSION: This study of nonradiolabeled iothalamate clearance for the measurement of GFR in potential kidney donors established age-adjusted normal values. In healthy individuals, GFR cannot be estimated accurately using the abbreviated MDRD or Cockcroft-Gault prediction equations.