Background: In overt hypothyroidism (OH) anemia is common, while less frequently basophilia has been described. In subclinical hypothyroidism (SCH), however, data on the distribution of peripheral blood cells are lacking. Therefore, we evaluated the effects of L-T4 replacement therapy on peripheral blood elements in female patients with SCH before and after restoration of euthyroidism in a randomized, double-blind and placebo-controlled study.
Patients and methods: Sixty-six women with SCH (TSH 12.9 +/- 8.2 mU/L) were randomly assigned to receive L-thyroxine or placebo for 48 weeks. 63 of the 66 women completed the study. Peripheral blood cells were measured at baseline and 48 weeks after L-thyroxine or placebo treatment, respectively.
Results: The percentage of lymphocytes decreased (p<0.05), whereas percent of monocytes (p<0.05) and eosinophiles (p<0.05) increased significantly upon restoration of euthyroidism after 48 weeks. Hemoglobin and hematocrit remained unchanged throughout the study period. However, erythropoietin levels increased significantly (p<0.01) during L-T4 treatment. In the placebo group all parameters remained unchanged throughout the study.
Conclusions: Overall, we observed subtle alterations of the leuco-lympho-monocytic distribution of the peripheral blood cells upon restoration of euthyroidism in patients with SCH. Hemoglobin and Hematocrit remained unchanged; however, the increasing level of erythropoietin during L-T4 treatment suggests an already stimulated, yet compensated erythropoietic system in mild thyroid failure.