Background: Thyroid hormones regulate metabolic rate and stimulate hematopoiesis via multiple mechanisms. Alterations in various hematological parameters have been reported in various thyroid disorders. Hypothyroidism is the most common thyroid disease. Objectives: To evaluate various erythrocyte indices and indices of iron metabolism in (subclinical and overt) hypothyroid cases and compare with control (euthyroid) group. Materials and Methods: Laboratory data and medical records of patients were retrieved. Patients were grouped as ‘overt hypothyroid’ (TSH >5.5 µIU/ml and reduced serum T4 and/or T3); ‘subclinical hypothyroid’ (TSH 4.0- 5.5 µIU/ml with normal thyroxin) and euthyroid (control) group (TSH 0.03-4.0 µIU/ml with normal serum THs). Complete blood count (CBC) and iron indices data of these cases were compiled. Statistical analysis was carried out using IBM SPSS version 25.0 statistical software. Result: 158 euthyroid, 56 subclinical hypothyroid and 28 overt hypothyroid cases were included.>70% of hypothyroid and ~60% of control group was anemic. Normocytic anemia was reported in 80% (overt) and 60% (subclinical) hypothyroid anemics, rest were microcytic. Reduced levels of TIBC;all erythroid markers {hemoglobin, TRBC, color index (CI), MCV, MCH, MCHC and PCV}, and significant increase in serum iron were observed in both subclinical and overt hypothyroid cases compared to euthyroid. Reduction of Hb, PCV, MCH and CI were statistically significant. These four parameters exhibited significant negative correlation with serum TSH whereas serum iron showed a significant positive correlation. Conclusion: Anemia cases (particularly treatment resistant ones) should be screened for thyroid abnormality. CBC should be carried out in all overt and subclinical hypothyroid cases.

Keywords: Color Index (CI); Mean Corpuscular Hemoglobin Concentration (MCHC); Subclinical Hypothyroidism (SCH); Total Iron Binding Capacity (TIBC); Thyroid stimulating hormone (TSH).