American Journal of Clinical Nutrition, Vol 64, 669-676, Copyright © 1996 by The American Society for Clinical Nutrition, Inc

ORIGINAL RESEARCH COMMUNICATIONS

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

CM Modlesky, RD Lewis, KA Yetman, B Rose, LB Rosskopf, TK Snow and PB Sparling
Department of Foods and Nutrition, University of Georgia, Athens, USA.

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 (DXAH) and the Lunar DPX-L (DXAL) dual-energy X-ray absorptiometry instruments. In addition, the ability of conversion equations to predict DXAH data from DXAL 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 DXAH and DXAL. Whereas measured body mass was not different (P > 0.05) between machines, whole-body fat mass [DXAH-DXAL (DXAdiff) = 1152 +/- 1395 g], percentage fat (DXAdiff = 1.5 +/- 1.7% of body mass), bone mineral density (BMD; DXAdiff = 0.016 +/- 0.023 g/cm2), and bone mineral content (BMC; DXAdiff = 316 +/- 50 g) were lower and whole-body fat- free soft tissue (FFST; DXAdiff = 1781 +/- 1859 g) was higher with DXAH than with DXAL. Lower fat mass (DXAdiff = 2145 +/- 855 g) and BMC (DXAdiff = 216 +/- 36 g) and higher FFST (DXAdiff = 1966 +/- 943 g) in the trunk were primarily responsible for the whole-body differences. Lower BMD and BMC values were found for LS (DXAdiff = 0.145 +/- 0.038 g/cm2 and 3 +/- 2 g, respectively), trochanter (DXAdiff = 0.100 +/- 0.044 g/cm2 and 1.7 +/- 1.0 g), and WT (DXAdiff = 0.195 +/- 0.061 g/cm2 and 1.93 +/- 0.51 g) with DXAH compared with DXAL. DXAH BMD of FN was also lower (DXAdiff = 0.141 +/- 0.032 g/cm2) than with DXAL. Only DXAH whole-body BMC and LS BMD were accurately predicted from DXAL with conversion equations. Predicted DXAH FN BMD was significantly lower than the actual DXAH value (P < or = 0.05), whereas the discrepancy between DXAH and DXAL actually increased for whole-body percentage fat and BMD (DXAdiff = 6.6 +/- 1.3% body mass and 0.020 +/- 0.025 g/cm2). In conclusion, lower whole-body fat mass, percentage fat, and BMC, and higher whole-body FFST with DXAH were due primarily to measurement differences in the trunk. Whereas conversion equations accurately predicted DXAH whole-body BMC and LS BMD from DXAL measurements in young adult males, they did not accurately predict DXAH, percentage fat, and BMD of the whole body and FN BMD.

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