The Effects of Iron Deficiency Anemia on Thyroid Function at Haematology Outpatient Department, BSMMU, Dhaka, Bangladesh

Objective: This study aimed to investigate the association between iron deficiency anemia and thyroid function among patients attending the Haematology Outpatient Department at Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh. Methods: This cross-sectional observational study included 120 patients with iron deficiency anemia (IDA) and 60 age- and sex-matched healthy controls. Complete blood count, iron profile (serum iron, total iron-binding capacity, transferrin saturation, and ferritin), and thyroid function tests (TSH, free T3, free T4, and anti-TPO antibodies) were performed. The severity of anemia was categorized as mild, moderate, or severe according to WHO criteria. Statistical analyses included comparative tests, correlation analyses, and multiple linear regression to evaluate the relationship between hematological parameters and thyroid function. Results: Patients with IDA had significantly higher TSH (3.82 ± 2.15 vs. 2.14 ± 1.08 mIU/L, p < 0.001) and lower free T3 (2.81 ± 0.63 vs. 3.34 ± 0.58 pg/mL, p < 0.001) and free T4 levels (1.05 ± 0.28 vs. 1.24 ± 0.23 ng/dL, p < 0.001) compared to controls. Subclinical hypothyroidism was present in 23.3% of IDA patients and 6.7% of controls, while overt hypothyroidism was found in 5.0% of IDA patients and none of the controls (p < 0.001). Thyroid function parameters showed significant correlation with hemoglobin, serum iron, transferrin saturation, and ferritin levels (all p < 0.05). A significant trend was observed in thyroid function abnormalities based on anemia severity, with more pronounced changes in severe anemia. Multiple regression analysis identified serum ferritin as the strongest independent predictor of thyroid function parameters (all p < 0.001). Conclusion: Iron deficiency anemia is associated with significant alterations in thyroid function, with the degree of dysfunction correlating with anemia severity. These findings suggest that thyroid function assessment should be considered in patients with iron deficiency anemia, particularly those with severe deficiency, to ensure comprehensive management of both conditions.