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 of 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 = 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.