Effect of hand positioning on iDXA total and regional bone and body composition parameters and precision error

Background: Dual energy X-ray absorptiometry (DXA) body composition measurements are performed in both clinical and research settings for estimations of total and regional fat mass (FM), lean tissue mass (LM) and bone mineral content (BMC). Subject positioning influences precision and positioning instructions vary between manufacturers. The aim of the study was to determine the effect of hand position and scan mode on regional and total body bone and body composition parameters and determine protocol-specific body composition precision errors. Methods: Thirty eight healthy subjects (men; mean age: 27.1 ± 12.1 years) received four consecutive total body (TB) Lunar iDXA (enCORE v 15.0) scans with re-positioning, and scan mode was dependent on body size. Twenty three subjects received scans in standard mode and fifteen received scans in thick scan modes. Two scans per subject were conducted with subject hands prone and two with hands mid-prone. The precision error (RMS-SD; %CV) and least significant change (LSC) for each protocol were determined using the International Society for Clinical Densitometry calculator. Results: Hands placed in the mid-prone position increased arm BMD (standard mode: 0.185 g*cm-2, thick mode: 0.265 g*cm-2; p < 0.05), total body BMD (standard mode: 0.051 g*cm-2, thick mode: 0.069 g*cm-2; p < 0.001) and total body BMD Z-score (standard mode: 0.5. thick mode: 0.7; p < 0.001). This was due to reductions in bone area and BMC. In standard mode, hands mid-prone reduced fat mass (0.05 kg, p < 0.05) and increased lean mass (0.11 kg, p < 0.05). There were no differences in body composition for thick mode scans. Hands mid-prone reduced lean mass precision error at the arms, trunk and total body (p < 0.01). Conclusions: DXA clinical and research centres are advised to maintain consistency in their hand positioning and scan mode protocols, and consideration should be given to the hand positioning used for reference data. As a best practice recommendation, published DXA-based studies and reports for clinic-based total body assessments should ensure that subject positioning is fully described.