HbA2 is a type of human hemoglobin, as there are three types of hemoglobin composed in normal adults: the first is HbA, or hemoglobin A, which is also the most common type of hemoglobin, accounting for about 95% or more of all hemoglobin. The second type is hemoglobin A2, which accounts for about 2-3% of all hemoglobin in peripheral blood. The third type is hemoglobin F, also known as fetal type hemoglobin. It is higher in the body during fetal life and decreases rapidly in concentration after birth. In adults, hemoglobin F does not exceed 1%. If the concentration of hemoglobin A2 increases in adults, this condition is commonly seen in certain patients with beta-thalassemia, and also in patients with beta-thalassemia if hemoglobin F is increased. By measuring hemoglobin A2, it has a certain guiding significance for the diagnosis of thalassemia.