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 ―

Abstract

Background: Low-triiodothyronine (T3) syndrome is a known complication in intensive care unit (ICU) patients, but the underlying mechanisms and prognostic impact are unclear. Methods and Results: 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 T3 [FT3] ≥1.88 µIU/L) and low-FT3 (n=759; FT3 <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 FT3. Survival rates (within 365 days) were significantly lower in the low-FT3 group. A multivariate Cox regression model showed that low FT3 was an independent predictor of 365-day mortality (hazard ratio 1.785; 95% CI 1.387-2.297). Low-T3 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-FT3 than normal group for patients with cardiovascular disease, particularly those with acute coronary syndrome and acute heart failure. Conclusions: Low-T3 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.