Comparison of Dual-Energy X-Ray Absorptiometry and Bioelectrical Impedance Analysis for Assessing Fat-Free Mass in Older Adults

ABSTRACT Dual-energy X-ray absorptiometry (DXA) is frequently used to assess sarcopenia and muscle mass in older adults. However, DXA is expensive, requires a licensed X-ray technician, and involves radiation exposure. In contrast, multi-frequency Bioelectrical Impedance Analysis (BIA) is quick, less-costly, requires no expertise, and does not involve radiation. Despite these practical advantages, comparative studies of DXA and BIA in healthy older adults are limited. PURPOSE: We compared DXA vs BIA for fat-free mass assessment and associations with power and strength in community-living older adults. METHODS: Community-dwelling older adults (N = 13, mean age = 68.5 years, 75% females) underwent both DXA and BIA measurements on the same day under standardized conditions. Muscle power and maximal strength were measured using a pneumatic leg press and physical function using a 30 sec chair stand. Spearman's correlations were used to assess associations and Intraclass correlation coefficient (ICC) was used to assess absolute agreement. Bland-Altman (BA) plot was used to evaluate measurement error and limits of agreement. RESULTS: Average fat-free mass (FFM) was 45.8 kg using DXA and 47.3 kg using BIA. FFM from both DXA and BIA showed similar correlations with muscle power (0.58 vs. 0.56), maximal strength (0.77 vs. 0.67), and chair stands (−0.34 vs. −0.40). Absolute agreement between the two methods was excellent, with an ICC of 0.95 (95% CI: 0.81, 0.98). BA plots showed a mean difference of 1.5 kg and limits of agreement of (-3.5, 6.5). CONCLUSION: Our findings demonstrate excellent agreement between DXA and BIA for FFM measurement in older adults, with both methods showing comparable associations with performance and functional outcomes. These preliminary findings are promising, but a larger sample size and longitudinal design are needed to draw stronger conclusions about the utility of BIA.