Comparing bedside and CT-derived muscle mass assessment methodologies at intensive care unit admission: A critical step towards bedside detection of reduced muscle mass.

The majority of included ICU patients had reduced skeletal muscle mass at admission.

• 56 ICU patients were included in the prospective, single-centre cohort study conducted between May 2023 and April 2025.
• 70% of patients were male.
• 64% of patients had reduced skeletal muscle mass as defined by CT-based SMI cut-offs (females <38 cm2/m2; males <50 cm2/m2).
• Patients were ≥18 years with an expected ICU stay ≥3 days.

CT-SMI showed only weak to moderate correlations with all bedside measurement parameters.

• Correlations of CT-SMI with BIA and US parameters ranged from r = 0.36 to 0.45, all p < 0.05.
• CT-SMI did not show strong correlation with any single bedside parameter.
• Bedside parameters assessed included BIA-derived skeletal muscle mass (BIA-SMM), fat-free mass (BIA-FFM), US-derived rectus femoris cross-sectional area (US-RFCSA), quadriceps muscle layer thickness (US-QMLT), and calf circumference (CC) adjusted for BMI.

CT-derived skeletal muscle area (CT-SMA) showed moderate correlations with BIA parameters but not with ultrasound or calf circumference measures.

• CT-SMA correlated moderately with BIA-FFM (r = 0.57, p < 0.001).
• CT-SMA correlated moderately with BIA-SMM (r = 0.62, p < 0.001).
• CT-SMA did not significantly correlate with US-RFCSA, US-QMLT, or CC (p > 0.05).

Sex-specific cut-off values for BIA-derived fat-free mass index (BIA-FFMI) and skeletal muscle mass index (BIA-SMMI) were identified for detecting reduced muscle mass at ICU admission.

• BIA-FFMI cut-offs were 23.8 kg/m2 for males and 20.0 kg/m2 for females.
• BIA-SMMI cut-offs were 13.4 kg/m2 for males and 10.7 kg/m2 for females.
• Cut-offs were derived using ROC analyses with CT-based SMI as the reference standard.
• Cut-offs were defined using established CT-SMI thresholds: <38 cm2/m2 for females and <50 cm2/m2 for males.

Cut-off values for adjusted calf circumference and ultrasound parameters were identified for detecting reduced muscle mass at ICU admission.

• Adjusted CC cut-offs were 36.8 cm for males and 33.8 cm for females.
• US-RFCSA cut-off was 4.3 cm2 (both sexes combined).
• US-QMLT cut-off was 2.3 cm (both sexes combined).
• These cut-offs were derived using ROC analyses.

Bedside assessments were performed within 48 hours of ICU admission and CT scans were retrieved from a window of 7 days before to 24 hours after ICU admission.

• Multifrequency BIA measurements were obtained within <48 hours of ICU admission.
• CT images used for L3 skeletal muscle index were retrieved from 7 days before to 24 hours after ICU admission.
• CT-derived measures included both skeletal muscle index (CT-SMI) and skeletal muscle area (CT-SMA) at the lumbar 3 (L3) level.
• This time window for CT acquisition may have introduced variability in the comparison between modalities.

Reduced skeletal muscle mass at ICU admission is associated with increased mortality, motivating the investigation of bedside detection methods.

• The study was motivated by the association between reduced skeletal muscle mass at ICU admission and increased mortality.
• CT scanning is the reference standard for muscle mass assessment but is not routinely performed at ICU admission for this purpose.
• Bedside techniques investigated as alternatives included BIA, ultrasonography, and calf circumference.
• The study aimed to determine both the accuracy of bedside methods compared to CT-SMI and to provide cut-off values for reduced muscle mass detection.