Disentangling the effects of fluid retention and low muscle mass on bioelectrical impedance–derived indices: A stratified analysis based on body water status

BACKGROUND & AIMS: ). METHODS: (below or above the median). Analysis of covariance (ANCOVA) was used to compare skeletal muscle mass index (SMI) and phase angle (PhA) across groups, adjusting for peak work rate (peak WR). Extended models additionally adjusted for sex, age, and N-terminal pro-B-type natriuretic peptide (NT-proBNP). RESULTS: . Bonferroni-corrected pairwise comparisons confirmed significant differences among all groups, indicating distinct contributions of fluid retention and muscle mass to BIA-derived SMI. For PhA, groups with higher ECW/TBW exhibited significantly lower adjusted PhA compared with those with lower ECW/TBW, regardless of TBW level. These findings remained consistent in extended ANCOVA models adjusting for sex, age, and NT-proBNP. No significant interactions between group and peak WR were observed for either SMI or PhA. CONCLUSIONS: allows discrimination between the effects of fluid retention and low muscle mass on BIA-derived indices. Higher SMI values and lower PhA values were observed in the presence of either fluid retention or muscle mass reduction, supporting the need for a multidimensional interpretation of BIA in these patients.