Levothyroxine Administration in Intensive Care Unit Patients with Low Thyroxine Levels: A Retrospective Comparison Study

Abstract Nonthyroidal illness syndrome is a common condition among intensive care unit patients. Previous studies showed conflicting findings regarding association with poor clinical outcomes. Studies examining whether levothyroxine administration improves clinical outcomes in critical patients with nonthyroidal illness syndrome and low free thyroxine levels are lacking. We aimed to examine whether levothyroxine administration in intensive care unit patients with the nonthyroidal illness syndrome and low thyroxine levels (< 0.8 ng/dL) resulted in differences in 28-day mortality and in-hospital morbidity. A retrospective study using electronic data retrieval for patients admitted to a general intensive care unit who presented with low free thyroxine levels and nonthyroidal illness syndrome. This study included 123 patients. A total of 53 patients received levothyroxine. No significant differences were found between groups regarding demographics, comorbidities or reasons for intensive care unit admission. Hospital length of stay was significantly longer in the treatment group (39±24 d) compared to that in the non-treatment group (30±19 d; p<0.05). The duration of mechanical ventilation was significantly longer in the treatment group (21±21 d) vs. non-treatment group (14±14 d; p<0.05). Intensive care unit length of stay showed a trend toward being longer in the treatment group (22±20 d) compared to that in the non-treatment group (16±13 d; p=0.058). Higher free thyroxine levels were associated with better clinical outcomes, including the reduced need for vasopressors and dialysis, and lower 28-day mortality. Low free thyroxine levels in intensive care unit patients with nonthyroidal illness syndrome are associated with higher morbidity. Levothyroxine administration did not improve clinical outcomes in this population.