ABO blood group system the precise glycosyl transferase set that confers the A, B and O epitopes. Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: "i", "I", and "I". The "I" designation stands for isoagglutinogen, another term for antigen. The gene encodes a glycosyltransferase—that is, an enzyme that modifies the carbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34). The "I" allele gives type A, "I" gives type B, and "i"
Blood transfusion by using blood type testing to identify a less scarce alternative. Jehovah's Witnesses object to blood transfusions due to their belief that blood is sacred. Although there are clinical situations where transfusion with red blood cells is the only clinically appropriate option, clinicians look at whether alternatives as feasible. This can be due to several reasons, such as patient safety, economic burden or scarcity of blood. Guidelines recommend blood transfusions should be reserved for patients with or at risk of cardiovascular instability due to the degree of their anaemia. In these cases parenteral iron is recommended. Thus far, there are