Factors of pre-existing low muscle mass and its relationship with mortality in critically ill patients: a sex-specific analysis.

OBJECTIVES: To investigate the factors, and mortality associations of pre-existing low muscle mass in ICU (intensive care unit) patients, with emphasis on sex-stratified analysis. METHODS: This cross-sectional study included 760 adult ICU patients (513 males, 247 females). Pre-existing low muscle mass was defined using sex-specific cutoffs based on CT. Multivariable logistic regression, restricted cubic spline (RCS) analysis were used to identify the factors associated with pre-existing low muscle mass. Cox proportional hazards models were applied to assess the association between pre-existing low muscle mass and 28-day mortality, adjusting for potential confounders. RESULTS: Among 760 ICU patients, pre-existing low muscle mass prevalence was 34.0% (males 41.3% vs. females 19.8%). Higher BMI was inversely associated with pre-existing low muscle mass in both sexes (males: aOR = 0.73, P < 0.001; females: aOR = 0.82, P < 0.001). High nutritional risk (NRS 2002 ≥ 4) and high comorbidity burden (aCCI ≥ 4) were independently associated with higher odds of pre-existing low muscle mass. Additioinally, RCS analysis revealed linear inverse BMI-pre-existing low muscle mass associations. Exploratory analysis suggested that the inverse association may plateau at higher BMI levels; however, these threshold values are hypothesis-generating and require prospective validation. In males, pre-existing low muscle mass was associated with higher 28-day mortality in unadjusted models, but these associations were attenuated after adjusting for confounders. CONCLUSIONS: BMI, nutritional risk, and comorbidity burden are key cross-sectional factors, which support early risk stratification using BMI, NRS 2002, and aCCI upon ICU admission. The exploratory plateau values are hypothesis-generating and need prospective validation.