A study published in the Journal of Clinical Endocrinology & Metabolism shows a 13.1% rate of thyroid dysfunction among patients with predominantly mild-to-moderate coronavirus disease 2019 (COVID-19).
“There may be a direct effect of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on thyroid function, potentially leading to exacerbation of pre-existing autoimmune thyroid disease. Low free triiodothyronine (fT3), associated with systemic inflammation, may have a prognostic significance,” wrote David Tak Wai Lui, Queen Mary Hospital, Hong Kong, China, and colleagues.
A total of 191 adult patients (mean age 53.5 ± 17.2 years; 51.8% male), without known thyroid disorders, admitted to Queen Mary Hospital for COVID-19 from July 21 to August 21, 2020 were included in the study. Most (84.3%) patients had mild disease, 12.6% had moderate disease and 3.1% had severe disease. None of the patients presented with overt symptoms of thyroiditis. Serum levels of thyroid-stimulating hormone (TSH), free thyroxine (fT4) and fT3 were measured in 191, 188 and 178 patients, respectively, on admission.
Overall, abnormal thyroid function tests (TFTs), defined by out-of-reference-range of TSH, fT4 or fT3 levels, were observed in 25 (13.1%) patients. Twelve (6.3%) patients had abnormal TSH, 12 (6.7%) had abnormal fT3 levels and 3 had abnormal fT4 levels. Meanwhile, 14 (7.3%) patients had features of thyrotoxicosis, defined as low TSH and/or raised fT4. Additionally, the researchers reported that 10 patients had isolated low TSH, suggestive of subclinical thyrotoxicosis due to thyroiditis, although they noted that the contribution of autoimmunity was likely in two of them and autoimmune thyroiditis probably also contributed to subclinical hypothyroidism in another patient. On the other hand, 10 patients had isolated low fT3 which, according to the authors, likely represents non-thyroidal illness syndrome.
When the researchers compared patients having normal TSH with those having subnormal TSH, more patients with subnormal TSH presented with fever (P = 0.030). In addition, more febrile patients had low fT3 (P = 0.015).
Further, study data showed a significant decreasing trend for fT3 levels with increasing disease severity (mild: 4.18 pmol/L, moderate: 3.83 pmol/L, severe: 3.68 pmol/L; P = 0.032), while median TSH and fT4 levels did not differ across disease severity. Multivariate logistic regression analysis revealed that a lower Ct value was independently associated with low TSH (P = 0.030) and higher CRP was independently associated with low fT3 (P = 0.007). Further, multivariable linear regression analysis showed that erythrocyte sedimentation rate (ESR) was independently associated with fT3/fT4 ratio.
Among 184 patients with available clinical outcomes, two patients died (1.1%) while 16 patients (8.7%) deteriorated clinically, defined as worsening in ≥1 category of clinical severity according to the Chinese National Health Commission guideline. The researchers found that patients with low fT3 were more likely to experience deterioration in clinical severity compared to those with normal fT3 (50.0% vs 5.0%, P < 0.001). Additionally, compared with those with normal fT3, more patients with low fT3 required dexamethasone and/or supplementary oxygen (41.7% vs 7.5%, P = 0.003) and prolonged hospital stay (≥14 days) (41.7% vs 12.7%, P = 0.018).
“Lower Ct values obtained from qualitative SARS-CoV-2 RT-PCR assays were associated with low TSH, while more systemic inflammation was associated with low fT3 and fT3/fT4 ratios. Both low TSH and low fT3 occurred more frequently among patients presented with fever,” the authors concluded. “Clinicians should be vigilant about the possible presence of thyroid dysfunction among COVID-19 patients, especially in the context of fever, lower Ct values and inflammatory markers. “