Context: The aims of the study are to compare characteristics of subacute thyroiditis (SAT) related to different etiologies, and to identify predictors of recurrence of SAT and incident hypothyroidism. Methods: This nationwide, multicenter, retrospective cohort study included 53 endocrinology centers in Turkey. The study participants were divided into either COVID-19–related SAT (Cov-SAT), SARS-CoV-2 vaccine–related SAT (Vac-SAT), or control SAT (Cont-SAT) groups. Results: Of the 811 patients, 258 (31.8%) were included in the Vac-SAT group, 98 (12.1%) in the Cov-SAT group, and 455 (56.1%) in the Cont-SAT group. No difference was found between the groups with regard to laboratory and imaging findings. SAT etiology was not an independent predictor of recurrence or hypothyroidism. In the entire cohort, steroid therapy requirement and younger age were statistically significant predictors for SAT recurrence. C-reactive protein measured during SAT onset, female sex, absence of antithyroid peroxidase (TPO) positivity, and absence of steroid therapy were statistically significant predictors of incident (early) hypothyroidism, irrespective of SAT etiology. On the other hand, probable predictors of established hypothyroidism differed from that of incident hypothyroidism. Conclusion: Since there is no difference in terms of follow-up parameters and outcomes, COVID-19– and SARS-CoV-2 vaccine–related SAT can be treated and followed up like classic SATs. Recurrence was determined by younger age and steroid therapy requirement. Steroid therapy independently predicts incident hypothyroidism that may sometimes be transient in overall SAT and is also associated with a lower risk of established hypothyroidism.

Background: Graves’ disease is an autoimmune thyroid disorder that may be accompanied by systemic inflammation and Graves’ orbitopathy. This study evaluated the relationship between readily available hematological inflammatory markers and orbitopathy in patients with Graves’ disease. Methods: This retrospective observational study included 178 adult patients with Graves’ disease. Demographic, clinical, ophthalmological, and laboratory data were analyzed. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), monocyte-to-HDL cholesterol ratio (MHR), and C-reactive protein-to-albumin ratio (CAR) were calculated. Correlation, logistic regression, and ROC analyses were performed. Results: Among the 178 patients, 63 (35.4%) had Graves’ orbitopathy. Patients with orbitopathy had significantly higher NLR, PLR, SII, MHR, and CAR values than those without orbitopathy (all p < 0.001). Thyrotropin receptor antibody (TRAb) and thyroid-stimulating immunoglobulin (TSI) levels were positively correlated with all inflammatory markers. In multivariable logistic regression analysis, current smoking (OR 2.31, p = 0.047), TRAb (OR 1.08, p = 0.009), TSI (OR 1.06, p = 0.041), NLR (OR 1.63, p = 0.034), SII (OR 1.01, p = 0.018), MHR (OR 2.91, p = 0.012), and CAR (OR 3.84, p = 0.008) remained independently associated with Graves’ orbitopathy. Among the individual biomarkers, MHR showed the highest discriminative performance (AUC 0.818, 95% CI 0.754–0.882), while the combined inflammatory model achieved an AUC of 0.891 (95% CI 0.842–0.940), with an optimal predicted probability cut-off ≥ 0.43. Conclusions: Hematological inflammatory markers are associated with thyroid autoimmunity, disease activity, and Graves’ orbitopathy. These inexpensive and easily accessible markers may support clinical risk assessment in patients with Graves’ disease.