- The A blood group is one of the four primary types in the ABO blood group system, a classification method based on specific antigens on the surface of red blood cells (RBCs) and corresponding antibodies in the plasma.
- People with blood group A have A antigens present on the surface of their red blood cells and produce anti-B antibodies in their plasma. These antibodies react against red cells that carry the B antigen, which is why individuals with type A blood cannot safely receive blood from group B or AB donors.
- There are two main variants of the A blood group, depending on the Rhesus (Rh) factor, which is an additional antigen found on red blood cells:
- A positive (A⁺): Indicates the presence of both A and Rh antigens on the RBCs.
- A negative (A⁻): Indicates the presence of A antigens but the absence of the Rh antigen.
- Transfusion compatibility for type A individuals depends on both ABO and Rh matching. For example, A-positive individuals can receive A⁺, A⁻, O⁺, and O⁻ blood, while A-negative individuals can safely receive only A⁻ and O⁻ blood. If blood from an incompatible group is transfused, the recipient’s immune system may attack the donor red cells, causing a hemolytic transfusion reaction, which can be life-threatening.
- Genetically, the A blood group arises from the presence of the A allele of the ABO gene, located on chromosome 9. The ABO gene has three main alleles: A, B, and O. The A allele is co-dominant with B and dominant over O. Thus, individuals with type A blood may have the genotype AA or AO.
- The distribution of blood group A varies among different populations and geographic regions. It is especially common in Europe and parts of Asia, with a significant proportion of individuals in those areas having A-positive blood. In contrast, its frequency is lower in many parts of Africa and among Indigenous populations in the Americas.
- In addition to its clinical importance in transfusion medicine, some studies have explored potential associations between blood group A and susceptibility to certain diseases. For example, people with blood type A may have a slightly increased risk for conditions like cardiovascular disease, gastric cancer, and certain infections, although these links are complex and influenced by many genetic and environmental factors.
