Comparison of body composition and bone mineral measurements from two DXA instruments in young men

The purpose of this study was to compare body-composition and whole-body, lumbar spine (LS), femoral:neck (FN), trochanter, and Ward's triangle (WT) bone mineral measurements by using the Hologic QDR 1000W (DXA(H)) and the Lunar DPX-L (DXA(L)) dual-energy X-ray absorptiometry instruments. In addition, the ability of conversion equations to predict DXA(H) data from DXA(L) data were tested. Thirteen healthy young adult males (aged 22.2 +/- 3.6 y, 177.4 +/- 5.3 cm in height, and 72.7 +/- 9.6 kg in weight) were scanned on the same day by using DXA(H) and DXA(L). Whereas measured body mass was not different (P > 0.05) between machines, whole-body fat mass [DXA(H) - DXA(L) (DXA(diff)) = 1152 +/- 1395 g], percentage fat (DXA(diff) = 1.5 +/- 1.7% of body mass), bone mineral density (BMC; DXA(diff) = 0.016 +/- 0.023 g/cm(2)), and bone mineral content (BMC; DXA(diff) = 316 +/- 50 g) were lower and whole-body fat-free soft tissue (FFST; DXA(diff) = 1781 +/- 1859 g) was higher with DXA(H) than with DXA(L). Lower fat mass (DXA(diff) = 2145 +/- 855 g) and BMC (DXA(diff) = 216 +/- 36 g) and higher FFST (DXA(diff) = 1966 +/- 943 g) in the trunk were primarily responsible for the whole-body differences. Lower BMD and BMC values were found for LS (DXA(diff) = 0.145 +/- 0.038 g/cm(2) and 3 +/- 2 g, respectively), trochanter (DXA(diff) = 0.100 +/- 0.044 g/cm(2) and 1.7 +/- 1.0 g), and WT (DXA(diff) = 0.195 +/- 0.061 g/cm(2) and 1.93 +/- 0.51 g) with DXA(H) compared with DXA(L). DXA(H) BMD of FN was also lower (DXA(diff) = 0.141 +/- 0.032 g/cm(2)) than with DXA(L). Only DXA(H) whole-body BMC and LS BMD were accurately predicted from DXA(L) with conversion equations. Predicted DXA(H) FN BMD was significantly lower than the actual DXA(H) value (P less than or equal to 0.05), whereas the discrepancy between DXA(H) and DXA(H) actually increased for whole-body percentage fat and BMD (DXA(diff) = 6.6 +/- 1.3% body mass and 0.020 +/- 0.025 g/cm(2)). In conclusion, lower whole-body fat mass, percentage fat, and BMC, and higher whole-body FFST with DXA(H) were due primarily to measurement differences in the trunk. Whereas conversion equations accurately predicted DXA(H) whole-body BMC and LS BMD from DXA(L) measurements in young adult males, they did not accurately predict DXA(H), percentage fat, and BMD of the whole body and FN BMD.