Abstract
Bioelectrical impedance analysis (BIA) is an accessible and cheap method to measure fat-free mass (FFM). However, BIA estimates are subject to uncertainty in patient populations with altered body composition and hydration. The aim of the current study was to validate a whole-body and a segmental BIA device against dual-energy X-ray absorptiometry (DXA) in colorectal cancer (CRC) patients, and to investigate the ability of different empiric equations for BIA to predict DXA FFM (FFMDXA). Forty-three non-metastatic CRC patients (aged 50-80 years) were enrolled in this study. Whole-body and segmental BIA FFM estimates (FFMwhole-bodyBIA, FFMsegmentalBIA) were calculated using 14 empiric equations, including the equations from the manufacturers, before comparison to FFMDXA estimates. Strong linear relationships were observed between FFMBIA and FFMDXA estimates for all equations (R2=0.94-0.98 for both devices). However, there were large discrepancies in FFM estimates depending on the equations used with mean differences in the ranges-6.5-6.8kg and-11.0-3.4kg for whole-body and segmental BIA, respectively. For whole-body BIA, 77% of BIA derived FFM estimates were significantly different from FFMDXA, whereas for segmental BIA, 85% were significantly different. For whole-body BIA, the Schols* equation gave the highest agreement with FFMDXA with mean difference ±SD of-0.16±1.94kg (p=0.582). The manufacturer's equation gave a small overestimation of FFM with 1.46±2.16kg (p<0.001) with a tendency towards proportional bias (r=0.28, p=0.066). For segmental BIA, the Heitmann* equation gave the highest agreement with FFMDXA (0.17±1.83kg (p=0.546)). Using the manufacturer's equation, no difference in FFM estimates was observed (-0.34±2.06kg (p=0.292)), however, a clear proportional bias was detected (r=0.69, p<0.001). Both devices demonstrated acceptable ability to detect low FFM compared to DXA using the optimal equation. In a population of non-metastatic CRC patients, mostly consisting of Caucasian adults and with a wide range of body composition measures, both the whole-body BIA and segmental BIA device provide FFM estimates that are comparable to FFMDXA on a group level when the appropriate equations are applied. At the individual level (i.e. in clinical practice) BIA may be a valuable tool to identify patients with low FFM as part of a malnutrition diagnosis.
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