Abstract: Background: Hypothyroidism is frequently associated with iron deficiency, but serum ferritin is not routinely assessed in thyroid evaluation. Understanding ferritin’s role could improve diagnosis and management.

Objectives: To assess the association between serum ferritin levels and hypothyroidism, evaluate gender differences, and compare ferritin in subclinical and overt hypothyroidism.

Methods: A prospective case-control study with 100 hypothyroid patients and 100 euthyroid controls matched by age and gender was conducted. Serum ferritin, thyroid-stimulating hormone (TSH), and free thyroxine (free T4) were measured. Statistical analyses included t-tests and Pearson correlations.

Results: Hypothyroid patients showed significantly lower ferritin levels (25.2 ± 10.1 ng/mL) than controls (60.3 ± 15.0 ng/mL, p < 0.001). Ferritin correlated inversely with TSH (r = –0.42, p < 0.001) and positively with free T4 (r = 0.38, p < 0.001). Female hypothyroid patients had lower ferritin than males (22.5 ± 9.8 vs. 30.1 ± 8.5 ng/mL, p = 0.01). Ferritin was lower in overt hypothyroidism compared to subclinical cases (21.8 ± 8.7 vs. 29.6 ± 11.0 ng/mL, p = 0.02).

Conclusion: Serum ferritin is significantly reduced in hypothyroidism, especially among females and in overt disease, and correlates with thyroid hormone status. Ferritin measurement should be incorporated into thyroid evaluation to detect iron deficiency early and optimize patient management.