Characteristics of anemia in subclinical and overt hypothyroid patients

Thyroid hormones stimulate directly or indirectly growth of erythroid colonies through erythropoietin. Anemia is often the first sign of hypothyroidism. Hypothyroidism can cause a wide variety of anemic disorders. Numerous mechanisms are involved in the pathogenesis of these anemias that can be microcytic, macrocytic and normocytic. We designed this study to investigate the anemia frequency and if present, etiology of anemia in hypothyroid patients. 100 patients with overt hypothyroid, 100 patients with subclinical hypothyroid, and 200 healthy controls were enrolled in this study. Overt hypothyroidism diagnosis is done when elevated TSH and low levels of free T4 and/or free T3 have been observed. Subclinical hypothyroidism is defined as elevated serum TSH with normal free T(4) and free T(3) levels. Peripheral smears of the anemic patients were examined. Anemia prevalence was 43% in the overt hypothyroid group, 39% in the subclinical hypothyroid group, and 26% in the control group (p=0.0003 and p=0.021 respectively related to controls). Thus, the frequency of anemia in subclinical hypothyroidism is as high as that in overt hypothyroidism. There was no difference between the hypothyroid groups in terms of anemia. Vitamin B12, Fe, and folic acid were similar between these groups. According to our findings, anemia of chronic disease is the most common type of anemia in hypothyroid patients. Suspicion of hypothyroidism should be considered in anemias with uncertain etiology.