The use of bioelectrical impedance analysis to predict total body water in patients with cancer cachexia.

The applicability of bioelectrical impedance analysis (BIA) to predict total body water (TBW) was assessed in 16 underweight [< 95% of ideal body weight (IBW)] and 25 normal-weight (> 95% of IBW) cancer patients. Although height2/resistance (ht2/R) proved to be a strong single predictor of TBW measured by deuterium dilution in both groups (normal-weight patients: r2 = 0.85, SEE 2.16 L; underweight patients: r2 = 0.86, SEE 2.24 L), TBW would be significantly overestimated in the underweight group if the prediction formula developed in the normal-weight group was used [bias 1.67 L (5%), 95% CI 0.20-3.15 L]. A systematic overestimation of TBW in the underweight patients was also found when TBW was predicted in our two patient groups by several previously published BIA formulas developed in normal-weight individuals. We conclude therefore, that although a similar relationship is found between ht2/R and TBW in normal-weight and underweight cancer patients, single-frequency BIA overestimates TBW in underweight patients when prediction formulas are used that have been developed in normal-weight subjects.