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Validity of Bioelectrical Impedance Analysis for the Assessment of Body Composition in Patients With Systemic
Lucas Denardi Dória1,2, Rafaela Cavalheiro do Espírito Santo3, Vanessa Hax1
1Division of Rheumatology, Hospital de Clínicas de Porto Alegre (HCPA), Porto Alegre, Rio Grande do Sul, Brazil.
Background:
Systemic sclerosis (SSc) is an autoimmune disease characterized by vasculopathy and progressive fibrosis. Reduced muscle mass is common and contributes to myopenia, sarcopenia and adverse clinical outcomes. Dual-energy X-ray absorptiometry (DXA) is the most widely used method in clinical research and is recommended by international guidelines as the reference standard for muscle mass evaluation in sarcopenia. However, its accessibility in routine clinical practice is limited. Bioelectrical impedance analysis (BIA) is a validated method for assessing body composition due to its affordability, ease of use and non-invasive nature. Nevertheless, variability across devices and assessment protocols may influence measurement accuracy, underscoring the need for validation in specific clinical populations. This study compared body composition measured by BIA and DXA and evaluated the diagnostic accuracy of BIA for detecting myopenia in SSc.
Methods:
In this cross-sectional study, patients with SSc underwent body composition assessment by BIA (InBody 370 s) and DXA (Lunar Prodigy Primo). Fat mass (FM), fat mass index (FMI), fat-free mass (FFM), fat-free mass index (FFMI), appendicular skeletal muscle mass (ASM), appendicular skeletal muscle mass index (ASMI) and ASM adjusted by body mass index (ASM/BMI) were assessed. Myopenia was defined according to established muscle mass criteria. Agreement was evaluated using Bland-Altman analysis and Lin's concordance correlation coefficient (CCC). Diagnostic performance was assessed using receiver operating characteristic (ROC) curves.
Results:
One hundred patients with SSc were included (91% women; mean age 60.1 ± 11.5 years; median disease duration 11.5 [5.0-20.3] years). Disease subtypes comprised 23% diffuse cutaneous, 61% limited cutaneous and 16% sine scleroderma. BIA demonstrated excellent agreement with DXA (CCC > 0.900) for ASM/BMI [Δ = 0.032; 95% CI 0.019-0.045], FM (Δ = -0.401; 95% CI -0.804 to 0.003), FMI (Δ = -0.190; 95% CI -0.366 to -0.015) and FFM (Δ = -0.010; 95% CI -0.415 to 0.395). Good concordance (CCC 0.750-0.900) was observed for ASM (Δ = 0.803; 95% CI 0.518-1.088). In women, ROC analysis showed high discriminative ability, with AUCs of 0.956 (95% CI 0.908-1.000) for ASM, 0.878 (95% CI 0.763-0.993) for ASMI and 0.969 (95% CI 0.935-1.000) for ASM/BMI. The optimal ASM/BMI cut-off (0.506) yielded 100% sensitivity and 90.1% specificity (PPV 55.6%, NPV 100%).
Conclusion:
BIA showed high agreement with DXA and strong diagnostic accuracy for detecting myopenia in SSc, particularly in women. These findings support BIA as an accessible tool for body composition assessment in SSc when standardized conditions and validated sex-specific cut-offs are applied.
