Bioelectric impedance spectroscopy underestimates fat-free mass compared to dual energy X-ray absorptiometry in incurable cancer patients

Background/Objectives: Weight loss is frequently seen in advanced cancer. Bioelectrical impedance spectroscopy (BIS) is a convenient method for estimating body composition. We examined in a prospective, comparative study if BIS could accurately estimate fat-free mass (FFM) in cancer patients compared to dual-energy X-ray absorptiometry (DXA). Subjects/Methods: The study was based on 132 consecutive incurable cancer patients with solid tumours in a University hospital outpatient clinic. Comparison of FFM from DXA and BIS with standard and revised equations. Bland-Altman plots, t-tests and linear regression analysis were used to evaluate agreement and differences between methods. Results: BIS significantly underestimated mean FFM with 7.6 +/- 4.7 kg compared to DXA (P < 0.001). Bias was significantly correlated to % weight loss (r = 0.32), systemic inflammation as measured by C-reactive protein (r = 0.29),malnutrition as assessed by low insulin-like growth factor-1 (r = -0.23) and inversely to the per cent body fat estimated by DXA (P = -0.61) and body mass index (BMI; r = -0.30). Revised BIS equations taking BMI into account reduced bias significantly but still with great individual variation. Conclusions: BIS by standard equations grossly underestimates FFM compared to DXA in cancer patients. This bias is related to weight loss, malnutrition and systemic inflammation. Revised equations improved FFM estimates, but with large individual variation. Thus, BIS with standard equations is not suitable to estimate FFM in patients with cachexia, inflammation and malnutrition. European Journal of Clinical Nutrition (2009) 63, 794-801; doi:10.1038/ejcn.2008.35; published online 14 May 2008