The Misdiagnosis of Beta-Thalassemia Heterozygosity Led by Hyperthyroidism

Abstract

When patients have mild microcytic hypochromic anemia with slightly increased hemoglobin (Hb) A₂ fraction, the most likely diagnosis is beta-thalassemia heterozygosity. But herein we found a patient who had all these hematological parameters but did not have beta-thalassemia heterozygosity. He was a 14-year-old Thai who presented with fatigue and heat intolerance for 2 weeks. His physical examination revealed mild diffuse enlargement of thyroid gland. Blood tests showed Hb 120 g/L, mean corpuscular volume (MCV) 72.1 fL, mean corpuscular hemoglobin (MCH) 23.3 pg/cell, free triiodothyronine (FT₃) > 20 pg/mL, free thyroxine (FT₄) > 5.0 ng/dL, thyrotropin < 2.5 mIU/L, serum ferritin 51.3 µg/L, Hb A₂ 3.8%. Besides primary hyperthyroidism, he was diagnosed with beta-thalassemia heterozygosity. After being treated with antithyroid drug for 6 months, his blood tests showed subclinical hyperthyroidism, Hb 146 g/L, MCV 83.3 fL, MCH 26.3 pg/cell, Hb A₂ 3.0%. Not only the thyroid hormones levels but also the Hb concentration, MCV, and the Hb A₂ percentage became normal. Due to this inconsistency, the DNA analysis for beta-thalassemia genes was performed and found negative for numerous common and rare beta-thalassemia genes meanwhile beta-globin gene sequencing appeared normal. It should be concluded that hyperthyroidism could induce slightly elevated Hb A₂ percentage and mild hypochromic microcytic anemia in a normal individual, leading to the misdiagnosis of beta-thalassemia heterozygosity. In other words, Hb analysis should not be performed during hyperthyroidism and it should be delayed till achievement of the euthyroid stage.