Associations of Phase Angle, GLIM-Defined Malnutrition, and Rectus Femoris Ultrasound with 30-Day Mortality in Critically Ill Adults: A Prospective Cohort Study

Background and aims: Early phenotyping in the ICU is challenging because severity scores do not capture malnutrition, cellular integrity, or muscle reserve. We assessed whether phase angle (PhA), GLIM-defined malnutrition, and rectus femoris ultrasound were associated with 30-day mortality and whether continuous PhA added prognostic information beyond illness severity. Methods: We analyzed a prospective single-center cohort of adults admitted to a 12-bed ICU. Within 24–48 h, patients underwent bioelectrical impedance analysis, rectus femoris ultrasound, GLIM, mNUTRIC, CONUT, APACHE II, and SOFA assessment. Primary multivariable analyses treated PhA and rectus femoris cross-sectional area (CSA) as continuous variables; ROC-derived cut-offs were considered exploratory. Potential non-linearity was examined with restricted cubic splines, and the continuous PhA model underwent bootstrap internal validation. Results: Among 125 patients (63.2% men; median age 68 [60–76] years), 30-day mortality was 24.0% (30/125). GLIM-defined malnutrition was present in 78.4%, including 12.0% with severe malnutrition. Non-survivors had lower PhA (4.3 [3.6–4.8] vs. 4.8 [4.2–5.5]°; p = 0.008) and smaller rectus femoris CSA (2.6 [1.9–3.4] vs. 3.6 [2.5–5.0] cm2; p = 0.007). In the adjusted continuous PhA model, APACHE II (OR 1.23 per point, 95% CI 1.13–1.34; p < 0.001) and severe GLIM-defined malnutrition (OR 5.95, 95% CI 1.45–24.32; p = 0.013) remained independently associated with mortality, whereas lower PhA did not (OR 1.11 per 1° lower, 95% CI 0.74–1.69; p = 0.611). Adding continuous PhA to the reference model changed AUC from 0.868 to 0.867 and did not improve fit (likelihood ratio p = 0.607). Continuous CSA was also not independently associated with mortality (OR 1.17 per 1 cm2 lower, 95% CI 0.81–1.69; p = 0.412). Conclusions: APACHE II and protocol-defined severe GLIM malnutrition, but not continuous admission PhA or rectus femoris CSA, retained independent associations with 30-day mortality; the GLIM association should be interpreted in light of the protocol-specific morphofunctional operationalization of the muscle criterion. Lower PhA and CSA characterized non-survivors in unadjusted analyses; cohort-derived thresholds should be considered hypothesis-generating and require external validation.