This study was designed to evaluate the levels of thyroid hormones in COVID-19 patients during the active period of the disease and one month after recovery. Our results showed that the levels of TSH in both males and females decreased during the active period of COVID-19 infection in comparison to the control group, while in the follow-up period, an increase was observed in the level of this hormone. In line with our study, Wang et al. studied 84 hospitalized COVID-19 patients and found that the levels of TT3 and TSH in these patients were lower compared with healthy people (p < 0.001) . Few cases of subacute thyroiditis (SAT) accompanying COVID-19 infection have been reported since the onset of the COVID-19 pandemic . Khatri et al. in their study explained a case of COVID-19 infection that manifested SAT without any clinical, or radiological cause of this other than COVID-19 were negative . Furthermore, Muller et al. in their study in hospitalized patients who affected with COVID-19 infection found that patients with more severe disease showed thyrotoxicosis and low level of TSH that might be resulted from SAT induced by COVID-19 infection . Our results are line with above-mentioned studies.
Our results showed that the levels of TT3 and TT4 were high during the active period of infection which fell significantly in the follow-up period. Similar to our results, Weiwei et al. in their study on 1395 individuals found that the level of FT4 increased and level of TSH and FT3 decreased significantly in patients with COVID-19 infection .
Chen et al. conducted a retrospective study on 50 patients and found that lower TSH was present in 56% of COVID-19 patients, and their levels of TT3 was lower compared with healthy people. Based in their results, the more severe the disease, the lower the level of thyroid hormones. They concluded that thyroid hormone levels were more likely to change in people with severe COVID-19 disease . Also, Wang et al. conducted a study on 84 hospitalized COVID-19 patients and found that the level of TT3 and TSH were significantly decreased during the active period of COVID-19 infection . Our results are similar to Chen et al. and Wang et al. except for that the level of TT3 in our study was higher in the active period of the disease and then reduced. The increase in the level of TT3 was negligible and even was much closed to the level of this hormone in the healthy individuals (1.20 ± 0.24 vs. 1.28 ± 1.25, p = .188). In our study, patients underwent corticosteroid therapy from the admission to hospital that may cause these manifestations.
The mechanism of change in thyroid hormones in infectious diseases is unknown. Studies have shown that the cause of changes in the level of thyroid hormones especially TSH during infectious diseases may not related to the pituitary origin, and may result from outside of pituitary such as bone marrow . At the present time there is no evidence in favor of direct thyroid effect of cytokines on thyroid hormones . Other studies explained the role of angiotensin-converting enzyme 2 (ACE2) receptors in the entry of viruses into the thyroid cells and cytokine storm . Also, apoptosis may play a role in the thyroid dysfunction associated with SARS disease .
In our study, 35 patients (44.8%) had a severe form of disease and were admitted to ICU, that none of them died. Patients with severe disease had non-significant lower levels of TSH at baseline. These results are in line with those of Chen et al . Also, Beltrao et al. reported that FT3 levels were lower in patients with severe disease, while the serum reverse triiodothyronine (rT3) was elevated in patients with severe disease. They drew the conclusion that thyroid hormones have a correlation with severity of the disease . The results of the present study are in line with those of Beltrao et al’s. In line with our study, Yazan et al. found that there is a relationship between changes of thyroid hormones and mortality in patients with COVID-19 infection, in this way that patients with higher reduction in TSH, FT3, and higher level of FT4 were more likely to admit to ICU or die .