ABO Blood Group System

1. Genetic Basis

• The ABO blood group system is determined by antigens (AGs) on the red blood cell (RBC) membrane and antibodies (ABs) in the plasma.

• The gene responsible for the ABO blood group is located on chromosome 9, with three alleles: IA, IB, and IO.

• The IA allele codes for AG A, the IB allele codes for AG B, and the IO allele does not code for any AG.

• AG A and B are also present in saliva, white blood cells, platelets, epithelium, and blood vessel endothelium.

2. Antigen Structure

• The precursor of ABO AGs is H AG, which appears in the fetus from the 5th-6th week, increases gradually, and stabilizes at the age of 2-4.

• H AG has a sugar chain structure consisting of glucose, galactose, N-acetyl glucosamine, and fucose.

• AG A is formed when the IA gene encodes the enzyme that adds N-acetylgalactosamine to the existing H AG.

• AG B is formed when the IB gene encodes the enzyme that adds D-Galactose to the existing H AG.

• Blood group O does not have AG A and B but is H AG.

3. Antibodies

• The formation of ABs in plasma in infants starts from 2-8 months, increases gradually and reaches its peak at 8-10 years old, then gradually decreases over time.

• Determining the blood group in infants from 4-6 months requires attention to the activity of antiA and antiB ABs. If high, it may be due to immune ABs from the mother transmitted through the placenta.

• The nature of naturally occurring antiA and antiB ABs is immunoglobulin M (IgM), produced and maintained by the body’s immune cells throughout life, and does not cross the placenta.

• The nature of immune antiA and antiB ABs is immunoglobulin G (IgG), formed after an immune response, and crosses the placenta.

4. Bombay Blood Group

• The Bombay blood group is a special case, lacking H, A, and B AGs.

• Individuals with the Bombay blood group do not agglutinate with antiA, antiB, and antiH ABs, but have antiA, antiB, antiH ABs in their plasma.

• This blood group is rare (1/7600) and is inherited in a recessive manner.

5. Blood Group Determination Methods

• Blood group determination is performed through two methods: red blood cell test (forward test) and serum test (reverse test).

• Forward test determines the AGs on the red blood cell membrane by adding standard ABs to the blood to be tested.

• Reverse test determines the ABs in plasma by adding known AGs to the blood.

6. Rh System

• The Rh system is determined by D, E, c, e, and d AGs.

• Individuals with D AG are called Rh+, those without D AG are Rh-.

• In the Rh+/-, plasma, no naturally occurring antiD ABs are present.

• Acquired antiD ABs appear after mismatched blood transfusions. The transfusion reaction does not occur in the first transfusion, but it will be stronger in subsequent transfusions.

• Rh determination is only through agglutination reactions with antiD ABs.

7. Blood Transfusion Principles

• The principle of blood transfusion is to transfuse the same blood group or to transfuse different groups but ensure that the AGs on the donor’s RBC membrane are not agglutinated by the corresponding ABs in the recipient’s blood.

• Blood group O can donate to all other blood groups, blood group AB can only receive AB blood.

• Blood transfusion requires a cross-match reaction before transfusion, the correct volume of blood, and transfusion rate.

8. Blood Transfusion in the Rh System

• It is recommended to transfuse the same Rh blood group.

• Rh- individuals can donate to Rh+, but Rh+ individuals cannot donate to Rh-.

9. Chemical Structure of Antigens

• O AG has an oligosaccharide structure consisting of glucose, galactose, acetylglucosamine, galactose, and fucose.

• AG A has the same structure as O AG but with an additional N-acetylgalactosamine.

• AG B has the same structure as O AG but with an additional galactose.

Note: This article is a summary, so it may not include all detailed information. Please refer to medical literature for more information.