Accuracy of measurements of small changes in soft-tissue mass by dual-energy x-ray absorptiometry

Objective: To assess the ability of dual-energy x-ray absorptiometry (DXA) to measure accurately small changes in lean soft-tissue mass. DXA has recently been suggested as an accurate, noninvasive method for analysis of body composition. Design: Experimental use of DXA to assess human body composition before and after rapid saline infusion. Participants: Six healthy men. Outcome measures: Weight measurements, DXA scanning results and skinfold thicknesses taken on the first day of the experiment and on the second day, before and after rapid saline infusion. Results: After the infusion, the subjects' weight increased by a mean 2.26 kg (standard deviation 0.199 kg). At each of the four readings, there was a strong correlation between weight and DXA-derived total mass (r = 0.999) and between skinfold-derived fat-free mass and DXA-derived lean mass (r = 0.941 to 0.957). Following infusion, no differences were found between the measured and theoretical (i.e., preinfusion value plus weight change) values for total mass (p = 0.22), lean soft-tissue mass (p = 0.10) and lean mass (p = 0.09). The bias was -0.669 (95% confidence interval [CI] 0.18 to -1.49) for total mass, -0.65 (95% CI 0.16 to -1.47) for lean soft-tissue mass, and -0.14 (95% CI 0.11 to -0.38) for lean mass. Conclusions: DXA is an improvement over previous dual-energy technologies and appears to provide sufficient accuracy to detect small (less than 2.5 kg) changes in mass in individual, healthy men, over a short period and under non-steady-state conditions. Therefore, DXA may also be of practical use for longitudinal assessment of weight change.