Background and objectives: Measuring body composition is relevant in geriatric medical patients at high risk of sarcopenia (loss of muscle mass/strength) for diagnosis and monitoring efficacy of treatment interventions. Dual-energy X-ray absorptiometry (DXA) and bio-impedance-analysis (BIA) are widely used in research/clinical practices, but their agreement is unknown in this population. Therefore, it was investigated how a dual-frequency (DF)-BIA compares to DXA regarding replicability, direct comparisons, and monitoring of total/segmental body composition in geriatric medical patients.

Methods: Measurements were taken while admitted to the geriatric medical ward and repeated 12 weeks after discharge for monitoring. Total population and gender-specific analyses were made.

Results: Thirty-one participants were included (age: 82±6 years, BMI: 26.2±4.3), and ten lost to follow-up. Replicability was high for both methods (R² ; 0.956, 0.999, p < 0.0001, n = 31), however, with wide 5th-95th-percentile ranges for individual agreement. Bland Altman plots revealed significant fixed systematic and negative proportional biases for body composition variables - both for the direct comparisons (e.g. total LBM, 1.2 kg higher with DF-BIA, p < 0.05, n = 31) and for monitoring (total LBM, kg; men (n = 15): DXA (0.96±2.61) vs. DF-BIA (-0.35±3.52) and women (n = 16): DXA (-0.39±1.51) vs. DF-BIA (-1.05±2.24)). Generally, correlations for direct comparisons were higher than for monitoring (R² ; 0.870, 0.947 vs. 0.048, 0.717 (head-region not included), n = 31).

Conclusion: DF-BIA and DXA cannot be used interchangeably in geriatric medical patients. However, high replicability shows that both methods may be used for monitoring under standardized conditions. Results indicate gender-specific differences, and segmental analysis can only be recommended with DXA using clear anatomical references.