Association between serum free triiodothyronine (FT₃) levels and ICU-acquired weakness: A prospective observational...

Intensive care unit-acquired weakness (ICU-AW) is a common complication among critically ill patients. Existing evidence indicates that critically ill patients frequently develop low triiodothyronine syndrome (LT₃S), and this thyroid hormone imbalance may disrupt muscle metabolic pathways and thereby promote the onset and progression of ICU-AW. However, the relationship between FT₃ levels and ICU-AW remains inconclusive, and clinical research addressing this link remains limited. Accordingly, this study aims to examine the clinical relationship between FT₃ levels and ICU-AW.

We enrolled patients with mechanical ventilation in the ICU of the Second Affiliated Hospital of Harbin Medical University from June 2024 to December 2025, dividing them into low-T₃ group (n=46, FT₃<2.43pmol/L) and non-low T₃ group (n=33, FT₃≥2.43pmol/L) by admission FT₃ levels. ICU-AW was defined as a Medical Research Council score≤48. We collected clinical data including demographics, comorbidities and laboratory results, compared baseline characteristics, and adopted correlation, regression and subgroup analyses to assess relevant associations.

Among 79 patients, 58.2% had reduced admission FT₃, and its incidence decreased with increasing MRC scores. Spearman analysis showed FT₃ levels were positively correlated with MRC scores. Fully adjusted logistic regression confirmed FT₃ as a factor associated with ICU-AW (OR=0.31; 95% CI, 0.10-0.97; p=0.0447). ROC analysis indicated FT₃ had good discrimination for ICU-AW (AUC=0.84).

Reduced FT₃ levels are closely associated with the development of ICU-acquired weakness, with higher FT₃ levels showing a positive correlation with higher MRC scores and a negative correlation with the risk of ICU-AW.

The study has been registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2500100201, registration date: April 3, 2025). This study is a retrospective registration.