COVID-19 infection and thyroid function

COVID-19 is a new viral infection affecting mainly the respiratory system with involvement of many other organs. Thyroid dysfunction has been described in COVID-19 but data are still unclear and conflicting on its frequency, severity and relationship with the outcome.

We assessed thyroid function tests (TFT) in 50 patients admitted to our institution with confirmed COVID-19 infection. We excluded patients known to have thyroid diseases or taking drugs that may affect thyroid function. Serum free thyroxine (FT4), thyrotropin (TSH) and triiodothyronine (T3) were measured once or more during the first 10 days after admission. In about 50 % of the cases, a follow up TFT was obtained during the first year after discharge (at a median follow up of 6 months).

We included 50 patients, 29 males (58 %) and 21 females (42 %). The median age was 47 years (range 25-89). Overall, TFTs were completely normal in all patients except for minor transient abnormalities in 5 patients (10 %) as follows: three patients had a mild transient elevated TSH, one had a mild transient suppressed TSH and one patient had a mildly low FT4 with normal TSH. There were no differences between the follow up TFTs obtained after discharge and TFTs obtained during admission in the acute phase.

In this study, thyroid dysfunction during acute COVID-19 infection was rare, mild and transient. However, the study might not be powered enough to detect an association between thyroid dysfunction and the severity of illness and further studies are needed to assess this issue. Late-onset thyroid dysfunction does not seem to occur in COVID-19 infection during the next year after discharge.