0326 - Principles of Transfusion Medicine Flashcards
Why is matching blood groups important in transfusion medicine?
Blood contains naturally occurring antibodies (ABO, RhD, Duffy etc), to which the ‘owner’ has developed tolerance. These antibodies form the basis of the blood groups, so by matching blood groups, you reduce the likelihood of an acute haemolytic (essentially allergic) reaction to the transfused blood or plasma.
Which blood type is the universal donor for red cells? Universal Recipient?
O is universal donor (no A or B antigens on the cells)
AB is universal recipient (no antibodies to A or B, so can take O, A, or B blood).
Which blood type is the universal donor for plasma? Universal Recipient?
AB is universal donor (contains no A or B antibodies, so anyone can take it)
O is the universal recipient (everybody has developed tolerance to the O antigen)
How is tolerance to ABO developed?
At birth there are no endogenously produced antibodies.
Gut colonisation leads to exposure to bacterial antigens similar to ABO.
Tolerance is developed for those antigens that the individual has, but if they don’t have them, they will be recognised as foreign.
Therefore, universal immunity against non-self ABO.
What is the difference between ABO and other blood groups?
ABO can lead to an haemolytic reaction in the first instance.
Most other significant antigen systems require prior exposure to red cells (e.g. previous transfusion, feto-maternal haemorrhage in RhD).
What are the three main types of blood reactions?
Acute haemolytic transfusion reaction
Delayed haemolytic transfusion reaction
Haemolytic disease of the newborn.
Describe an acute haemolytic transfusion reaction
Most commonly due to ABO incompatibility, and due to clerical error.
Immediate antigen/antibody binding, complement activation and intravascular haemolysis
Signs - Urticaria (hives), chest pain, hypotension, diffuse intravascular coagulation, haemoglobinuria, acute renal failure.
Remains one of most common causes of transfusion-related death.
Treatment is resuscitation.
Describe a delayed haemolytic transfusion reaction (general).
More common, less severe, than acute reaction.
Triggered by memory B cells, which raise antibody levels (not detected pre-transfusion) - anamnestic
Red cells are coated with IgG and removed by the reticuloendothelial system.
Jaundice and fall in Hb occur 7-10 days following transfusion.
Describe the immunological process of a delayed haemolytic transfusion reaction.
An individual receives red cells that are positive for a specific antigen for which they are negative.
If this is the first exposure, the red cells survive, but stimulate antibody production. At 3 months, the antibody is present, but doesn’t cause harm as no transfused RBCs remain.
Over time, antibody levels fall, but memory B cells remain. If subsequent transfusion with the same antigen occurs, patient gets an anamnestic response.
Increased production of antibody, agglutinates and opsonises cells.
Cells removed by reticuloendothelial system, and haemolysis.
Describe haemolytic disease of the newborn.
Antigen usually (not always) RhD: Rh- Mother, Rh+ foetus.
Bleed from foetus to mother (particularly at delivery), results in RhD being introduced, and antibody formation.
If this happens in subsequent pregnancies, IgG can cross placenta, causing haemolysis in foetus or newborn.
Leads to anaemia, hydrops, foetal demise, hyperbilirubinaemia, and kernicterus.
Prevented by vaccination with pre-formed antibodies. Destroy antigenic RBCs before immune response.
What is the direct antiglobulin (Coomb’s) test?
Test for detecting haemolytic anaemia.
Sample from Pt with haemolytic anaemia (so antibodies on RBCs) is combined with Coomb’s reagent.
Coomb’s reagent contains anti-IgG Ig’s, causing agglutination of those RBC’s that are already coated in antibodies.
What is the indirect antiglobulin (Coomb’s) Test
Test for preventing adverse transfusion reactions.
Recipient serum is combined with donor RBCs, and will form antibody-antigen complexes if the recipient would have an adverse reaction. Coomb’s reagent is then added to the solution, agglutinating any RBC’s that have the complexes.
No agglutination = no antibody against those RBC’s.
