Comparison of dual-energy X-ray absorptiometry to four other methods to determine body composition in underweight patients with chronic gastrointestinal disease.

Assessment of body composition may provide important information about the nutritional status. The applicability of two safe and convenient methods for body composition analysis, bioelectrical impedance analysis (BIA) and dual-energy x-ray absorptiometry (DXA), in underweight patients with chronic gastrointestinal disease has been sparsely elucidated. Our objective was to compare measurements by DXA with four other methods. Furthermore, we compared total body water (TBW) by BIA using three different BIA equations with measurement of TBW by tritium dilution (TBW-3H2O). Nineteen clinically stable underweight patients with chronic gastrointestinal disease were included in the study (body mass index [BMI], 19.3 +/- 1.2 kg/m2). Body composition was assessed using total body potassium (TBK), isotope dilution of tritium (3H2O), anthropometry (skinfold thickness [SF]), BIA, and DXA. Fat-free mass (FFM) by DXA was in reasonable agreement with body composition measurements by TBK (mean difference(TBK-DXA) = -1.61 kg, r = .88, standard error of the estimate [SEE] = 4.66 kg) and 3H2O (mean difference(3H2O-DXA) = 0.98 kg, r = .93, SEE = 3.34 kg). Although mean values for FFM by DXA differed significantly versus BIA and SF, we found highly significant correlations between the measurements (r = .97 and r = .97, respectively). The mean TBW by BIA was overestimated by 1.9 and 3.1 L compared with TBW-3H2O when prediction equations for normal-weight subjects were used. We conclude that the DXA method is a valuable addition to the list of methods available for body composition studies in clinically stable underweight patients. Our data show that BIA equations for normal-weight subjects overestimated TBW in the patients studied.