Thyroid Function, Reverse Triiodothyronine, and Mortality in Critically Ill Clinical Patients

BACKGROUND: To evaluate the association of thyroid hormones changes, including increased reverse triiodothyronine (rT3) level, with critically ill clinical patients´ mortality. PATIENTS AND METHODS: This study analyzed the observational data prospectively collected over 8 months (2018) in an adult intensive care unit (ICU) in Brasilia, Brazil. All consecutive ICU-admitted clinical patients were included. Thyroxine (T4), free thyroxine (fT4), triiodothyronine (T3), free triiodothyronine (fT3), rT3, and thyroid-stimulating hormone (TSH) were collected within 48 hours of ICU admission. Patients with hypothyroidism or hyperthyroidism who were previously diagnosed were excluded. RESULTS: Of 353 included patients, age was 68.5 ± 19.0 years, sequential organ failure assessment (SOFA) score was 3.3 ± 2.9, and Acute Physiology and Chronic Health Evaluation II (APACHE II) was 17.1 ± 7.9. ICU mortality was 17.6% (n = 62). Non-survivor patients had a higher incidence of increased rT3 (69.3 vs 59.2%, p = 0.042), lower incidence of low T4 (4.8 vs 9.7%, p = 0.045), and increased age (75.2 ± 16.3 years vs 67.1 ± 19.3 years, p = 0.001), SOFA (3.0 ± 0.4 vs 2.8 ± 2.6, p <0.001), and APACHE II (23.5 ± 7.5 vs 15.7 ± 7.2, p <0.001). Alterations in other thyroid hormones did not show association with mortality. Increased rT3 [odds ratio (OR): 2.436; 95% confidence interval (CI): 1.023–5.800; p = 0.020] and APACHE II (OR: 1.083, 95% CI: 1.012–1.158; p = 0.044) were associated with ICU mortality in the multivariate analysis. CONCLUSION: Increased rT3 was independently associated with increased ICU mortality. In contrast, other thyroid hormone alterations did not show an association with mortality. Determining rT3 levels may be a helpful test to identify an increased risk for ICU mortality in clinical patients. HOW TO CITE THIS ARTICLE: da Silveira CDG, de Vasconcelos FPJ, Moura EB, da Silveira BTG, Amorim FFP, Shintaku LS, et al. Thyroid Function, Reverse Triiodothyronine, and Mortality in Critically Ill Clinical Patients. Indian J Crit Care Med 2021;25(10):1161–1166.