Thyroid dysfunction as a long-term post-COVID-19 complication in mild-to-moderate COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), may lead to thyroid disorders, including both thyrotoxicosis and suppression of thyroid function. The aim of the present study was to assess the post-COVID-19 effects on thyroid function in patients without history of thyroid disease after complete recovery from mild-to-moderate COVID-19. Thyroid function tests [thyroid-stimulating hormone (TSH), free thyroxine (fT4), antithyroid antibodies] were performed on 113 patients (median age of 43.0 years; 31.0% male) two months after initial SARS-CoV-2 infection. TSH and fT4 were determined again one month later in this observational, prospective study. Thyroid dysfunction was registered in 61.1% of the patients (78.3% subclinical hypothyroidism, 13% subclinical hyperthyroidism and 8.7% overt hypothyroidism) two months after COVID-19. Moderate rather than mild manifestation of COVID-19 was significantly associated with a higher risk of thyroid dysfunction (OR 5.33; 95% CI: 1.70-16.69, p = 0.002), presence of thyroglobulin antibodies and need for levothyroxine therapy. At the follow-up, the subclinical hypothyroidism persisted in 28.3% of the subjects. Moreover, the TSH level was significantly reduced in comparison to the second month after the initial COVID-19 infection in all the patients (p < 0.001), but not in those with subclinical hypothyroidism and without hormone replacement therapy. Our findings indicate that COVID-19 could have long-term, negative effects on thyroid function. Therefore, thyroid function testing should be included in the follow-up algorithm of COVID-19 survivors.