Removal of body surface area normalisation improves raw-measured glomerular filtration rate estimation by the Chronic Kidney Disease Epidemiology Collaboration equation and drug dosing in the obese

Abstract

Background/Aim: We aimed to compared estimated glomerular filtration rate (eGFR) according to the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI), with (mL/min/1.73m2) and without body surface area (BSA) normalisation (CKD-EPI_noBSA, mL/min) against measured 99m Technetium - diethylenepentaacetic acid (Tc-DTPA GFR) (mL/min) in 222 individuals, including 80 with malignancy. Methods: BSA was calculated for each individual using the Du Bois equation. The CKD-EPI and CKD-EPI_noBSA equations were compared with measured Tc-DTPA GFR with respect to bias, proportion within 30% of GFR (P30) and root mean square error for predicting levels of GFR, and concordance in relation to carboplatin dosing. Results: The mean (SD) for BSA and measured GFR for the entire group was 1.99 (0.25) m2 and 127 (41) mL/min respectively. The P30 for Tc-DTPA GFR was significantly higher with the CKD-EPI_noBSA (80%) than with the CKD-EPI equation (63%, P = 0.0001). In those with body mass index (BMI) > 30kg/m2, the P30 values for the CKD-EPI_noBSA and CKD-EPI were 74% and 42% respectively (P < 0.0001). Carboplatin dosing concordance for the cancer patients using the CKD-EPI and CKD-EPI_noBSA equation was 71% and 56% respectively (P = 0.07). In 78 individuals with BMI > 30kg/m2, concordance in relation to carboplatin dosing using CKD-EPI_noBSA was 65% compared with 26% with the CKD-EPI (P < 0.0001). Conclusion: The CKD-EPI without normalisation (CKD-EPI_noBSA) equation was superior to the CKD-EPI equation in estimating raw-measured Tc-DTPA GFR (mL/min).