HBA is hemoglobin A, which is the most important hemoglobin component in the human body, accounting for about 95% or more of all hemoglobin in the human body, and it consists of a pair of alpha peptide chains and a pair of beta peptide chains. Because the body’s hemoglobin includes hemoglobin A, hemoglobin A2 and hemoglobin F, and each hemoglobin is composed of hemoglobin and bead protein peptide chains, hemoglobin A is two alpha peptide chains and two beta peptide chains. Of these, hemoglobin A2 accounts for 2-3% of all human hemoglobin, while fetal hemoglobin accounts for only about 1% of all hemoglobin. Normal HBA makes up more than 95% of all hemoglobin. If the level of HBA decreases, it means that the level of hemoglobin A2 or hemoglobin F is elevated, which is most commonly seen in beta thalassemia.