Does COVID-19 Infection Change Thyroid Hormone Levels? A Comparative Cross-Sectional Study in Iran

Background: There is a paucity of research investigating the changes in thyroid hormones in individuals affected by coronavirus disease 2019 (COVID-19). Objectives: This study aimed to evaluate the levels of thyroid hormones in individuals affected by COVID-19 infection in Ahvaz, Iran. Methods: This was a comparative cross-sectional study on 78 patients with COVID-19 infection and 80 individuals without infection. Thyroid-stimulating hormone (TSH), triiodothyronine (TT3), and tetraiodothyronine (TT4) were measured in hospitalized patients at baseline and one month after recovery and in participants without infection. The data were analyzed using a paired t-test, the Chi-square test, the Wilcoxon test, and the analysis of covariance (ANCOVA). Results: The level of TSH at baseline in the hospitalized patients was significantly lower than that in the control group (1.24 ± 1.08 vs. 2.05 ± 1.02 mlU/L, respectively, P < 0.0001). The mean level of TT3 was 1.20 ± 0.24 and 1.28 ± 1.25 ng/dL in the case and control groups, respectively (P = 0.188). The level of TT4 in the case group was high at baseline in comparison to the control group (8.48 ± 2.27 vs. 7.76 ± 1.43 ng/dL, P = 0.076), which was reduced in the follow-up period. Thirty-five (44.8%) patients had severe disease and were admitted to the intensive care unit (ICU). The level of TSH was non-significantly lower in patients with severe disease than those with moderate disease. Conclusions: Patients with COVID-19 infection showed abnormalities in thyroid hormones, such as decreased levels of TSH and TT3. Patients with severe COVID-19 showed lower levels of TSH and unchanged levels of TT3 and TT4 in comparison to the patients with moderate disease. Further investigation into thyroid function in patients with COVID-19 is recommended.