Table 1.
Causes of variation in the percentage of hemoglobin A2.
| Hb A2 | Inherited | Acquired |
|---|---|---|
| Increased (>3.4%) | β-Thalassemia heterozygosity Deletional HPFH from Vietnamese/South East Asian Hereditary high Hb A2 Unstable hemoglobin Sickle cell trait Sickle cell anemia (particularly coexisting α-thalassemia) Hb S/β0-thalassemia Congenital dyserythropoietic anemia (some cases) Heterozygosity for other β-chain variants |
Thyrotoxicosis HIV infection Zidovudine therapy Megaloblastic anemia (some cases) |
| Decreased (<2.2%) | α-thalassemia: α+ homozygosity, a0 heterozygosity, and HbH disease Deletional HPFH (except Vietnamese/South East Asian type) δβ and Aγδβ-thalassemia heterozygosity (some cases) δ-Thalassemia Hemoglobin Lepore Hemoglobin Kenya |
Severe iron deficiency Anemia of chronic disease Sideroblastic anemia Lead poisoning Juvenile myelomonocytic leukemia Acquired Hb H disease Acute myeloid leukemia (some cases, particularly erythroleukemia) Aplastic anemia (some cases) Hypothyroidism Chemotherapy-induced increased Hb F synthesis |
Hb A2 – hemoglobin A2; HPFH: hereditary persistence of fetal hemoglobin; HIV: human immunodeficiency virus; HbH: hemoglobin H; Hb F: hemoglobin F or fetal hemoglobin.
Source: Modified from Bain et al.4