7.3 ABO - Tagged

The ABO Blood Group

Introduction to ABO Blood Group System

The ABO blood group system is a classification system for blood based on the presence or absence of antigens on the surface of red blood cells. This system was discovered in the early 20th century by Karl Landsteiner and has profound implications in blood transfusions and organ transplantation. The existence of different blood types not only affects transfusion compatibility but also plays a critical role in medicine, anthropology, and genetics.

Genetic Basis of ABO Blood Groups

ABO Blood Groups Represent:

The ABO blood group system consists of four main blood types: A, B, AB, and O, which are determined by the presence of antigens on the erythrocyte membrane. The genetic basis of these blood groups arises from multiple alleles:

• IA (A Antigen): Indicates the presence of A antigens on the surface of red blood cells.

• IB (B Antigen): Indicates the presence of B antigens on the surface of red blood cells.

• i (O): Indicates the absence of A and B antigens, leading to the O blood type.

Complete Dominance:

• IA is completely dominant to i, meaning that only one copy of the IA allele is needed for an individual to express the A antigen. Therefore, individuals with IAi or IAIA genotype will have type A blood.

• IB is completely dominant to i, therefore, those with IBi or IBIB genotypes will express the B antigen, typifying blood type B.

Co-dominance:

In the case of a heterozygote (IAIB), where both IA and IB alleles are present, both A and B antigens are expressed simultaneously.

• The phenotype exhibits characteristics of both alleles, resulting in the AB blood type, which contains both A and B antigens on the cells.

• Importantly, IA and IB are co-dominant to each other, which means that individuals with this genotype will have a unique blood type distinct from A and B.

ABO Blood Types and Blood Transfusions Outcomes

ABO Blood Types:

Understanding the distribution and occurrence of different blood types (A, B, AB, O) is crucial, as each type is associated with specific genetic and evolutionary traits. Globally, blood type frequencies vary significantly among different populations.

Blood Transfusion Outcomes:

Matching blood types during transfusions is essential to prevent serious complications, such as hemolytic reactions. If a person receives blood containing antigens that their immune system recognizes as foreign (e.g., type A blood for a type O individual), their body can mount an immune response, leading to dangerous and potentially fatal results.

• Therefore, blood type compatibility is a critical aspect of safe medical practices during transfusions and surgeries that require direct blood donations.

• Understanding these risks not only underlines the importance of blood typing but also advances medical knowledge in immunohematology, emphasizing the need for precise blood matching.