Association of COVID-19 Infection with Subsequent Thyroid Dysfunction: An International Population-Based Propensity...

Background: The COVID-19 pandemic's impact on thyroid function is a growing concern. Previous studies have produced inconclusive results, and there is a lack of comprehensive research into the long-term risks of thyroid dysfunction following COVID-19 infection. Methods: In this retrospective cohort study, we used data from the TriNetX international database, which includes electronic health records from a broad, diverse patient population. We compared patients with COVID-19 (cases) to those without (controls), matching for age, sex, race, and comorbidities using propensity score matching. The primary outcome was the diagnosis of thyroid dysfunction (thyrotoxicosis or hypothyroidism) within a 12-month period, analyzed using hazard ratios (HRs) and Kaplan-Meier curves, and stratified by age and sex. Results: Initially, the study included 1,379,311 COVID-19 patients and 6,896,814 non-COVID-19 patients from the TriNetX database. After matching, the cohorts were comparable in demographics and baseline characteristics. This study consistently demonstrated a significant increase in the risk of thyroid dysfunction, including thyrotoxicosis and hypothyroidism, among COVID-19 patients compared to non-COVID-19 patients. In the short term (3 months postexposure), the COVID-19 group exhibited a HR of 2.07 (95% confidence interval [CI] 2.01-2.12) for thyroid dysfunction, which included both thyrotoxicosis (HR 2.10, CI 1.92-2.29) and hypothyroidism (HR 2.08, CI 2.01-2.13). This heightened risk persisted over the long term (up to 12 months), with HRs indicating an ∼2.01-fold increased risk for overall thyroid dysfunction, a 1.8-fold increased risk for thyrotoxicosis, and a 2.04-fold increased risk for hypothyroidism. Subgroup analysis, stratified by age and sex, revealed a notably higher risk of thyroid dysfunction in patients aged 65 and above (HR 2.18, CI 2.11-2.25), compared to those in the under-65 age group (HR 1.97, CI 1.91-2.03). Both male and female patients were associated with an elevated risk, with females showing a slightly higher association with thyroid dysfunction (HR 2.12, CI 2.06-2.16) compared to males (HR 1.76, CI 1.69-1.82). Conclusions: COVID-19 infection was associated with an increased risk of thyroid dysfunction, including thyrotoxicosis and hypothyroidism, regardless of age or sex, during a 12-month follow-up period. Further research is required to validate these findings.