Effect of Euthyroid Sick Syndrome Development on Prognosis in COVID-19 Patients

INTRODUCTION: Thyroid function tests may deteriorate as a result of coronavirus infection. Low free triiodothyronine(FT3) levels are related to a poor prognosis in patients with coronavirus disease 2019 (COVID-19) presenting with euthyroid sick syndrome(ESS). In this study, it was aimed to examine the mortality and other events that developed in the hospital and within the 2-year follow-up in patients who developed ESS.
METHODS: In this retrospective study, 170 patients who were hospitalized as a result of COVID-19 were included. The patients were divided into two groups, as those with ESS and those without(non-ESS), according to the reference range of thyroid-stimulating hormone(TSH), FT3, or free thyroxine(FT4) levels. Secondary events that developed during the hospitalization and/or long-term follow-up (mean 24 months) were analyzed from the hospital registry system.
RESULTS: ESS developed in 97 of a total of 170 patients. Of those, 84 died during hospitalization or within the 2-year follow-up. The FT3 and FT4 hormone levels were significantly lower in the ESS group (P<0.001 for both). The COVID-19-associated mortality ratio was significantly higher in the ESS group (P<0.001). Moreover, the occurrence of acute respiratory distress syndrome and acute renal failure was higher in the ESS group(P<0.05). The frequency of complications, such as acute myocardial infarction, acute heart failure, and atrial fibrillation, was similar between the groups.
DISCUSSION AND CONCLUSION: The development of ESS with low FT3 levels was associated with disease severity, increased mortality, and risk of complications in COVID-19 patients. The development of ESS is an important prognostic indicator in the course of COVID-19 in long-term follow-up.