Evaluation of Inflammatory, Immunonutritional, and Atherogenic Profiles in Patients with Hashimoto’s Thyroiditis

Background/Objectives: Hashimoto’s thyroiditis (HT) is associated with autoimmune thyroid inflammation, but its systemic inflammatory, immunonutritional, and atherogenic lipid profile across thyroid functional groups remains insufficiently characterized. This study aimed to evaluate routinely available inflammatory, immunonutritional, and atherogenic indices across the HT spectrum and to examine their relationships with thyroid function and autoimmunity. Methods: This retrospective study included newly diagnosed, untreated adult patients with HT and healthy controls without documented comorbidities. After exclusions and propensity score matching for age, sex, and body mass index, 148 patients with HT and 74 controls were analyzed. Patients with HT were classified as euthyroid HT (EH, n = 62), subclinical hypothyroidism (SCH, n = 47), or overt hypothyroidism (OH, n = 39). A total of 44 demographic, thyroid-related, hematologic, biochemical, lipid, inflammatory, immunonutritional, and atherogenic variables were evaluated. Elastic Net–penalized logistic regression, multivariable logistic regression, correlation analysis, and receiver operating characteristic curve analysis were performed. Results: HT was associated with a distinct systemic profile characterized by higher inflammatory and atherogenic indices and alterations in immunonutritional indices. Across the control, EH, SCH, and OH groups, systemic inflammation response index (SIRI; 0.5 vs. 0.8 vs. 1.0 vs. 1.4, p < 0.001) and atherogenic index of plasma (AIP; 0.1 vs. 0.3 vs. 0.5 vs. 0.8, p < 0.001) showed an ascending pattern, whereas prognostic nutritional index (PNI; 56.0 ± 3.2 vs. 50.2 ± 6.0 vs. 46.8 ± 5.5 vs. 40.6 ± 7.0, p < 0.001) showed a descending pattern. In multivariable models, SIRI and AIP were independently associated with EH compared with controls, whereas SIRI, AIP, and PNI were independently associated with SCH compared with EH and with OH compared with SCH. SIRI and AIP showed strong positive correlations with thyroid-stimulating hormone and negative correlations with free thyroxine, while PNI showed the opposite pattern. These indices also differed significantly according to anti-thyroid peroxidase and anti-thyroglobulin antibody status. Conclusions: Distinct inflammatory, immunonutritional, and atherogenic lipid profiles were observed across HT groups. SIRI and AIP may reflect systemic alterations even in EH, whereas lower PNI may reflect immunonutritional alterations associated with SCH or OH.