Estimated Lean Body Mass Is More Appropriate than Body Surface Area for Scaling Glomerular Filtration Rate and Extracellular Fluid Volume

Abstract

Background/Aims: To compare body surface area (BSA) with lean body mass (LBM) for scaling extracellular fluid volume (ECV) and glomerular filtration rate (GFR). Methods:Phase 1: Total body water (TBW), bromide space and LBM were measured with ³H-water, ⁷⁷Br and dual X-ray absorptiometry, respectively, in 6 healthy adults. Phase 2: ECV and GFR were measured with ⁵¹Cr-EDTA in 95 healthy adults and 56 children (0.5–13 years). ECV was calculated as GFR divided by GFR/ECV, both corrected for the one-compartment assumption. LBM was estimated (eLBM) in adults from height and weight and in children using a height/weight formula for estimating ECV and a constant derived from a separate adult population relating ECV to eLBM. Results:Phase 1: LBM and BSA correlated closely with TBW and bromide space. With LBM, the regressions passed through the origin, but with BSA, the intercepts were significantly below zero. Phase 2: GFR/BSA and ECV/BSA were higher in men than women but no difference was recorded in GFR/eLBM, GFR/ECV or ECV/eLBM. ECV showed a linear relation with eLBM and a non-linear relation with BSA. GFR/BSA and ECV/BSA correlated significantly with BSA but neither GFR/eLBM nor ECV/eLBM correlated with eLBM. Conclusion: eLBM is preferable to BSA for scaling GFR and ECV.