Blood Group and Typing - MBBS & BDS 1

Study Notes

Two main blood group systems: ABO and Rh.
ABO system is vital for transfusion therapy due to the presence of naturally occurring antibodies which can lead to severe transfusion reactions if mismatched.
Haemolytic disease of the foetus and newborn (HDFN) occurs when maternal antibodies cross the placenta and attack fetal red blood cells.

Antigens: Substances recognized as foreign; induce immune response.
Antibodies: Immune response products specifically reacting with antigens.
Agglutination: Clumping of red blood cells when antibodies bind to antigens on multiple cells.
Alloimmunization: Immune response to non-self antigens in the same species, often from transfusions.
Immunogenicity: Potential to provoke an antibody response, influenced by the antigen’s size and complexity.

Over 29 known blood group systems; 9 major systems identified: ABO, Rh, MNS, P, Kell, Duffy, Kidd, Lewis, and Lutheran.
Approximately 400 distinct blood group antigens described in these systems.
Significant in transfusion as individuals without certain antigens may develop antibodies leading to transfusion reactions.

ABO and Rh groups are the most clinically significant due to their strong immunogenic properties.
Some blood groups (e.g., Lewis) have reduced clinical importance, reacting at lower temperatures and presenting less frequently.
Patients needing repeated transfusions (e.g., Sickle Cell Disease, Thalassaemia) may be at risk for delayed hemolytic reactions due to these less common antigens.

Natural Antibodies: Develop early in life post-exposure to similar antigens, mainly IgM. Clinically significant examples: anti-A and anti-B from the ABO system.
Immune Antibodies: Form in response to transfusions or during pregnancy, primarily IgG, with anti-D from the Rh system being a notable example.

Considered the most critical blood group system for transfusions.
ABO genes are located on chromosome 9, controlled by alleles A, B, and O (O is recessive).
ABO blood types based on antigens and corresponding antibodies:
- Type O: Genotype OO, no antigens, has anti-A and anti-B antibodies (50% frequency in Malawi).
- Type A: Genotype AA or AO, A antigen, has anti-B antibodies (24% frequency).
- Type B: Genotype BB or BO, B antigen, has anti-A antibodies (22% frequency).
- Type AB: Genotype AB, AB antigens, no antibodies (4% frequency).

Composed of RhD and RhCE genes, featuring five antigens: D, C, c, E, e.
RhD is the most significant; presence indicates RhD positive, absence indicates RhD negative.
Rh antibodies develop from previous transfusions or pregnancies.

Performed in the laboratory to ensure safe transfusions:
- Grouping of ABO and RhD for the patient.
- Screening for antibodies in patient serum.
- Cross-matching between patient serum and donor red blood cells to verify compatibility.