Clinical Significance of Low-Triiodothyronine Syndrome in Patients Requiring Non-Surgical Intensive Care - Triiodothyronine Is a Comprehensive Prognostic Marker for Critical Patients With Cardiovascular Disease.

Low-triiodothyronine (T) syndrome is a known complication in intensive care unit (ICU) patients, but the underlying mechanisms and prognostic impact are unclear. This study retrospectively enrolled 2,976 patients who required care in the ICU. Of these patients, 2,425 were euthyroid and were divided into normal (n=1,666; free T [FT] ≥1.88 µIU/L) and low-FT (n=759; FT <1.88 µIU/L) groups. Multivariate logistic regression analysis revealed that prognostic nutritional index >46.03 (odds ratio [OR] 2.392; 95% confidence interval [CI] 1.904-3.005), age (per 1-year increase; OR 1.022; 95% CI 1.013-1.031), creatinine (per 0.1-mg/dL increase; OR 1.019; 95% CI 1.014-1.024), and C-reactive protein (per 1-mg/dL increase; OR 1.123; 95% CI 1.095-1.151) were independently associated with low FT. Survival rates (within 365 days) were significantly lower in the low-FT group. A multivariate Cox regression model showed that low FT was an independent predictor of 365-day mortality (hazard ratio 1.785; 95% CI 1.387-2.297). Low-T syndrome was significantly more frequent in patients with non-cardiovascular than cardiovascular diseases (73.5% vs. 25.8%). Prognosis was significantly poorer in the low-FT than normal group for patients with cardiovascular disease, particularly those with acute coronary syndrome and acute heart failure. Low-T syndrome was associated with aging, inflammatory reaction, malnutrition, and renal insufficiency and could lead to adverse outcomes in patients admitted to a non-surgical ICU.