A technique to assess body composition and sarcopenia using DXA: application for an obese population.

The objective of this study was to explore the accuracy of summing multiple dual-energy X-ray absorptiometry (DXA) scans to estimate whole-body soft tissue measures and the sarcopenic index in female subjects for application to an obese population. Forty-five women who fit within the DXA scanning region (M+/-s.d.; BMI=24.5+/-4.6 kg/m(2)) were scanned four times (one normal whole body (WB) scan, one head/trunk/leg scan allowing trunk delineation (TRK-H-L), one scan with body shifted right (LA) and one left (RA) to allow arm delineation). Fat mass (FM) and appendicular lean mass were determined from the WB scan (aLM(WB)), with the latter determined by summing arm and leg mineral-free lean mass (MFLM). Strong agreement and no differences (M+/-s.d.(DIFF)) were found between FM(WB) and FM(SUM) (-0.12+/-0.38 kg, P=0.37; r=0.999, P<0.001); MFLM(WB) and MFLM(SUM) (0.02+/-0.36 kg, P=0.80; r=0.998, P<0.001); and aLM(WB) and aLM(SUM) (0.12+/-0.32 kg, P=0.63; r=0.994, P<0.001). Summing DXA scans is a valid method for determining the risk for sarcopenic obesity and may aid research regarding obesity and risk for disability.

Location of body fat and body size impacts DXA soft tissue measures: a simulation study.

OBJECTIVE: The aim of this study was to determine the ability of dual X-ray absorptiometry (DXA) to detect exogenous fat in men and women simulating typical sex-specific weight changes. SUBJECTS: A diverse sample including 29 elderly (52-83 years) and 61 young (18-40 years) individuals (45 women, 45 men) of varying body mass index (BMI; M+/-s.d.: 26.1+/-4.9 kg/m2, range=16.4-39 kg/m2). METHODS: Whole body (WB) DXA scans (Hologic QDR 4500A) were completed with Scan 1 performed as a normal baseline scan, Scan 2 with 1 kg packet of lard placed on each thigh and Scan 3 with two 1 kg lard packets placed on the abdomen (men) or chest and abdomen (women). RESULTS: Measurement error of fat mass (FM) was more pronounced in the trunk as lard packets were detected with 59% accuracy (error=0.82+/-0.42 kg, P<0.001), whereas 94% of thigh lard (error=0.11+/-0.45 kg, P<0.001) was determined to be FM, while the remainder in both conditions was determined to be mineral free lean mass. Initial FM (r=0.37, P<0.001) for thigh loading and trunk bone mineral content (r=0.30, P<0.01) for trunk-loaded conditions had the most impact on measurement error of WB FM. CONCLUSIONS: Regional differences impact measurement error of simulated changes in FM with greater measurement error in the trunk compared to the thigh region and initial FM and higher levels of bone mineral content in the trunk region impacting error.