Hemoglobin A2 in hyperthyroidism.

Erythrocyte hemoglobin A2 (Hb A2) was quantitated in 28 hyperthyroid patients prior to antithyroid therapy and at intervals during therapy. Fetal hemoglobin (Hb F) levels and red cell mean corpuscular volume (MCV) were also monitored. Before therapy, Hb A2 was significantly elevated (mean +/- SD, 3.3 +/- 0.5%: normals, 2.5 +/- 0.3%: p less than 0.001). Hb F levels exceeded 1.0% in 10 cases. A tendency to red cell microcytosis was also observed (mean MCV 81.1 fl). To-date 10 of these subjects have had adequate studies following appropriate and sustained responses to antithyroid therapy. All showed a fall in Hb A2, usually accompanied by a rise in red cell MCV. A hematologic profile for hyperthyroidism is proposed.