Novel DXA body composition approaches: comparison with traditional total body scans

Traditionally, total body (TB) dual-energy x-ray absorptiometry (DXA) scans to assess body composition include the entire body, however novel abbreviated acquisition methods exist. The purpose of this study was to evaluate comparability of measured and estimated body composition results using three novel acquisition techniques; total body less head (TBLH), neck to knee (NTK) and lower extremity (LE). We hypothesized that body composition mass with these three novel methods would not differ from traditional TB acquisition.

Each subject had TB, TBLH, NTK and LE scans acquired using a Lunar iDXA. A subset of 30 had repeat NTK and LE scans with repositioning between and a matched historical precision control was compiled from existing data for comparison. TBLH and NTK scans used automated software to limit anatomy scanned; NTK estimated non-scanned lower leg mass. LE scans were acquired from L3 to just beyond the toes. Automated analysis, with manual correction, was used for all but LE scans, which were analyzed manually. Equivalence testing was used to compare regional lean, fat and bone mineral content (BMC) measurements from the novel scanning methods to traditional full TB scans. Precision was determined by the ISCD Precision Calculator and compared to TB historical precision by F-test.

The study sample included 82 subjects, 41F/41 M mean (SD) age 51.0 (18.4) years and BMI 25.5 (3.7) kg/m². Total and regional lean, fat and bone mass were equivalent among all approaches (p < 0.01). There was excellent agreement between sexes and ages with TB and TBLH (p < 0.001). Some clinically irrelevant disagreement was observed in NTK and LE fat and lean measurements while NTK and LE precision was excellent, ranging from 0.45 to 2.31%CV.

These three novel approaches provide regional body composition data consistent with traditional TB measurement and may be considered as equivalent substitutes when appropriate.