Role of dry lean body mass for estimation of glomerular filtration rate in kidney transplant recipients

Background: The use of equations that predict glomerular filtration rate (GFR) in patients with a kidney graft is still a matter of debate. The purpose of this study was to determine the level of accuracy of GFR equations and the relevance of dry lean body mass in the assessment of GFR. Methods: In a prospective clinical study, 100 patients with a kidney graft were included. Estimated GFR with Modification of Diet in Renal Disease equation (MDRD), Chronic Kidney Disease Epidemiology Collaboration equation (CKD EPI) with serum creatinine concentration (CKD EPI Cr), serum cystatin C concentration (CKD EPI CysC) or both (CKD EPI Cr-CysC), and creatinine clearance calculated with Cockcroft- Gault equation (CG) was compared with GFR measured by 51Cr-EDTA clearance (mGFR 51Cr-EDTA). Dry lean body mass (body mass without fat mass and body water) was measured with bioimpedance analysis. Results: All of the estimating equations overestimated mGFR 51Cr-EDTA by a significant degree (bias +/- SD in mL/min/1.73m(2), 30% accuracy in brackets): CG 16.8 +/- 14.1 (44%), MDRD 12.5 +/- 15.3 (54%), CKD EPI Cr 15.1 +/- 15.3 (50%), CKD EPI CysC 8.0 +/- 16.6 (56%), CKD EPI Cr-CysC 10.3 +/- 13.4 (55%). Dry lean body mass significantly correlated with mGFR 51Cr-EDTA, but not with estimated GFRs. Conclusion: The estimating GFR equations are neither accurate nor precise in renal transplant recipients. Dry lean body mass is an important parameter that could potentially improve the GFR estimation in this population.