Introduction: Kidney transplantation prolongs life expectancy in end-stage renal disease patients at a lesser cost than dialysis. Estimation of kidney function is crucial in the evaluation of prospective living kidney donors. Although unsurpassed in their precision methods of glomerular filtration rate (GFR) measurement with exogenous substances are invasive, expensive, and carry a risk for anaphylactic reactions. Alternatively, kidney function can also be assessed by GFR estimation formulas based on serum creatinine or novel markers such as cystatin C or β-trace protein (BTP). The aim of this study was to compare the performance of GFR estimation methods with reference scintigraphy-measured GFR in population of living kidney donor candidates.
Methods: We included 25 prospective kidney donors (aged 28-64 years) and measured GFR with the following equations: Cockcroft-Gault, Modification of Diet in Renal Disease (MDRD), Mayo Clinic, Nankivell, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI; including cystatin C), and BTP based. GFR were assessed by (99)mTc-DTPA for reference. All estimation methods were compared with a reference by general linear models.
Results: The precision of GFR estimation by all methods is unsatisfactory (30% margin of reference held in <50% of cases). Direction of regression coefficients is negative for some of the methods even when adjusted for body mass index (BMI). Of the study subjects, 64% were overweight/obese. BMI value is significantly correlated with measured GFR (P < .01). CKD-EPI estimation equations are the most precise methods of GFR estimation in this analysis; in addition, CKD-EPI cystatin C and combined creatinine/cystatin C estimators are robust to overweight/obesity.
Conclusions: The precision of GFR estimation is unsatisfactory, in part because of overweight, which adversely influences measured GFR, but also renders estimation methods unusable, except for CKD-EPI cystatin C and combined creatinine/cystatin C formulae. GFR measurement with exogenous substances remains the method of choice in the assessment of kidney function in prospective kidney donors. In addition, it provides useful information on differential (split) renal function.