Clinical and Hematological Characteristics of Vietnamese Heterozygous Hb Tak/β-Thalassemia Patients: A Four- Case Series

Hemoglobin Tak (Hb Tak) is an extremely rare high-oxygen-affinity β-globin variant, and data on heterozygous Hb Tak/β-thalassemia remain limited. We performed a retrospective analysis of four Vietnamese cases, reviewing clinical, hematological, and biochemical characteristics. Hemoglobin fractions were analyzed by high-performance liquid chromatography (HPLC), Hb Tak was confirmed by Sanger sequencing, and JAK2V617F mutation testing was used to exclude polycythemia vera (PV).All patients presented with erythrocytosis accompanied by microcytosis and hypochromia, elevated HbA₂ (>3.5%) and/or HbF, and a high proportion of abnormal hemoglobin on HPLC (76.6–83.6%). Serum erythropoietin levels were increased, and the JAK2V617F mutation was negative. Reduced iron stores were observed.Conclusion: This case series expands current knowledge of heterozygous Hb Tak/β-thalassemia. Erythrocytosis and microcytosis should prompt consideration of high-oxygen-affinity hemoglobin variants, not just PV with iron deficiency. Awareness of this distinctive hematological pattern may facilitate appropriate diagnostic evaluation and management, particularly in patients presenting with unexplained erythrocytosis.