The Blood Transfusion Laboratory

Question 1

Describe the 2 ways in which in vivo antibody-antigen reactions lead to cell destruction.

Answer 1

• Directly - cell breaks up in bloodstream - intravascular
• Indirectly - liver and spleen remove antibody-coated cells - extravascular

Question 2

What is agglutination and how is it used clinically in the lab?

Answer 2

• Agglutination is the clumping together of RBCs into visible agglutinates by antigen-antibody reactions.
• Agglutination results from antibody cross-linking with the antigens and occurs in vitro (in the lab).
• As the antigen-antibody reaction is specific, agglutination can identify the presence of a red cell antigen (i.e. blood group) or the presence of an antibody in the plasma (i.e. antibody screening/identification).

Question 3

Outline the inheritance of the ABO blood groups.

Answer 3

• A and B are codominant - i.e. AO or BO genotypes result in blood groups A and B respectively.
• AB genotype = AB blood group.
• O is recessive - i.e. blood group O is always OO genotype.

Question 4

Explain what is meant by the forward and reverse blood typing tests.

Answer 4

• Forward - patient’s red cells tested with serum containing anti-A, anti-B and anti-D antibodies.
• Reverse - patient’s plasma tested with A cells and B cells.

Question 5

Outline the Rh blood grouping system and the most common phenotypes.

Answer 5

• Rh system - over 50 antigens, D the most common.
• 85% of UK are RhD positive, 15% negative.
• 4 other main antigens - C, c, E and e.

Question 6

What is haemolytic disease of the newborn (HDN)?

Answer 6

• Rh- mother carrying first Rh+ foetus.
• Rh antigens can enter the maternal blood during delivery.
• Mother develops immune response - anti-Rh antibodies.
• IgG antibodies developed - can cross placenta.
• Second Rh+ foetus exposed to anti-Rh IgG.

Question 7

How is haemolytic disease of the newborn prevented?

Answer 7

• Rh negative mothers injected with small quantities of anti-Rh antibodies to remove any fetal Rh positive cells in the circulation.
• Maternal immune system will therefore not be exposed to enough Rh positive cells to stimulate production of anti-Rh antibodies.