COMPONENTS OF VARIANCE WHEN ASSESSING THE REPRODUCIBILITY OF BODY-COMPOSITION MEASUREMENTS USING BIOIMPEDANCE AND THE HOLOGIC QDR-2000 DXA SCANNER

This study evaluated the reproducibility of measuring lean tissue mass (LTM), fat mass (FMDXA), bone mineral content (BMC) and density (BMD) with a Hologic QDR-2000 DXA scanner, and both fat free mass (FFMbio) and fat mass (FMbio) with an impedance meter. Furthermore, the study a imed to assess whether sheets and pillows significantly altered the DX A results. Fifty-one healthy volunteers aged 20-61 years were examined before and after repositioning (n = 20), removal of the sheets (n = 1 0), addition of two foam pillows (n = 11) or a regular pillow (n = 10) . One to 7 days later a re-examination was performed (n = 35). Eight s urgical patients were also scanned twice 1-7 days apart. The day to da y coefficients of variation were about 1% for most measurements, thoug h more than 2% for FMDXA and FMbio. For total tissue mass, LTM, and BM C there was a significant biological day to day variance whereas for t he other measurements the day to day variation could be accounted for by just measurement variance. Pillows systematically changed the estim ates of bone mineral and soft tissue, but sheets did not.