HbA2 is hemoglobin A2, which is a type of human hemoglobin. In normal adults, hemoglobin A2 accounts for 2%-3% of all hemoglobin, and if hemoglobin A2 exceeds 5%, it may be beta-thalassemia. Because of β-thalassemia, the amount of hemoglobin A decreases due to a genetic mutation that causes an impairment in the synthesis of the β-jugin peptide chain. The decrease in hemoglobin A is followed by a corresponding increase in the concentration of hemoglobin A2. Therefore, a hemoglobin A2 concentration of more than 5% should be alerted to β-thalassemia. A small number of patients with pernicious anemia and patients with megaloblastic anemia due to folic acid deficiency may also have mildly elevated hemoglobin A2. For mildly elevated hemoglobin A2, serum folate and vitamin B12 tests should be performed to rule out pernicious anemia and megaloblastic anemia.