CRITICAL-ASSESSMENT OF BODY-COMPOSITION MEASUREMENTS IN MALNOURISHED SUBJECTS WITH CROHNS-DISEASE - THE ROLE OF BIOELECTRIC IMPEDANCE ANALYSIS

Bioelectric impedance analysis (BIA) has been widely used for assessment of body composition in healthy subjects but has not been validated in malnourished patients. This study compared calculation of fat-free mass (FFM) by five methods to determine whether the currently used equations for total body water (TBW) as assessed by BIA were applicable to 19 malnourished patients with Crohn's disease. When compared with TBW assessed by (H2O)-O-18 dilution, BIA was higher by 5.9 +/- 1.1% (P < 0.005). A stepwise-multiple-regression equation was derived to validate BLA: TBW (kg) = 0.25 (ht(2)/resistance) + 0.29 (wt) + 3.63 (r = 0.97, SEE = 0.28). Comparison of the hydration of FFM (TBW by O-18 dilution/FFM) between methods showed that total body potassium (TBK) gave a significantly higher value when compared with the reference method of body protein, mineral, and O-18 analysis. Dual-energy x-ray absorptiometry (DXA) provided a value for TBW/FFM in close agreement with the reference method. We conclude that BIA overestimates TBW, and TBK underestimates FFM in malnourished patients. DXA provides an accurate measurement of body fat in malnutrition.