ABO blood group system alleles in white individuals of the ABO gene that produce one's blood type: The same study also identified 18 rare alleles, which generally have a weaker glycosylation activity. People with weak alleles of A can sometimes express anti-A antibodies, though these are usually not clinically significant as they do not stably interact with the antigen at body temperature. Cis AB is another rare variant, in which A and B genes are transmitted together from a single parent. The distribution of the blood groups A, B, O and AB varies across the world according to the population. There are also variations
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