Use of dual-energy X-ray absorptiometry in obese individuals

Dual-energy X-ray absorptiometry (DXA) provides precise measurements of body composition in humans. Because its use in obese subjects is limited by the size of the scanning area, we explored the possibility of estimating whole-body composition from DXA half-body scans. Body composition of 183 subjects with a wide range of body sizes [body mass index (BMI; in kg/m2) of 17.7 - 52.8] was assessed by DXA and hydrodensitometry. Subjects fitting in the DXA scanning area (group A, n = 156) were scanned once whereas subjects exceeding it (group B, n = 27) were scanned twice, once for each side of the body. When body-composition results for the right and left sides were compared, only minimal differences between the two sides of the body were found in both groups. Least-squares-regression analysis of whole-body composition by hydrodensitometry on DXA gave the following results: percent body fat, r2 = 0.89 (SEE = 4.1%); fat-free mass, r2 = 0.89 (SEE = 3.72 kg); and fat mass, r2 = 0.95 (SEE = 3.57 kg). Similar r2 values and SEEs were obtained for percent body fat when only results from DXA half-body scans of all subjects were considered: right side, r2 = 0.90 (SEE = 4.1%); and left side, r2 = 0.89 (SEE = 4.2%). The error in predicting body composition by hydrodensitometry from DXA whole- or half-body scans was not affected by the subject's body size and/or scanning technique. In conclusion, our results indicate that half-body scan values by DXA accurately predict whole-body composition.