Hemoglobin A is the most important component of human hemoglobin, because human hemoglobin is composed of three kinds of proteins, including hemoglobin A, which accounts for more than 95% of all human hemoglobin, and hemoglobin A2, which accounts for 2%-3% of all human hemoglobin, and fetal hemoglobin, or hemoglobin F, which is less than 1% of total hemoglobin in adults. Because human hemoglobin is composed of hemoglobin and pearl protein, there are two kinds of pearl protein, one is alpha peptide chain and the other is non-alpha peptide chain, and hemoglobin A is composed of alpha peptide chain and beta peptide chain. If the level of hemoglobin A decreases in the human body, it often represents a disease called beta thalassemia. Beta thalassemia is a genetic disease caused by the deletion of beta peptide chain, and there is a decrease of hemoglobin A accompanied by an abnormal increase of hemoglobin F.