Haem: Blood Transfusions Pt.1 Flashcards
What proportion of population are RhD negative?
15%
What type of antibodies are anti-RhD?
IgG
Therefore can cross the placenta
Describe how the consequences ABO incompatibility are different to rhesus incompatibility.
- ABO - immediated haemolytic transfusion reaction (can be fatal)
- Rhesus - delayed haemolytic transfusion reaction
Why does rhesus incompatibility cause delayed haemolysis?
Because IgG-binding leads to extravascular haemolysis
IgG activates complement less that IgM
List some other antigens that can lead to transfusion reactions.
- Rhesus C, c, E, e
- Kell (K), Duffy and Kidd (particularly important for delayed transfusion reactions)
What is a dangerous consequences of rhesus incompatibility in a pregnant woman?
Haemolytic disease of the newborn
How is the patient’s blood group tested?
- Anti-A, anti-B and anti-D reagents are mixed with the patient’s red blood cells
- A positive result means that the red cells will float to the top of the vial (agglutination)
Takes 10 minutes - done before every transfusion
How can the types of red blood cell antibodies in the patient’s serum be identified?
Known A and B group red blood cells are mixed with the patient’s plasma (which contains IgM antibodies)
Describe how the antibody screen of a patient’s plasma works.
- Conducted using the indirect antiglobulin test (IAT)
- 2 or 3 reagent red blood cells are used which contain all the important red cell antigens
- The patient’s serum is incubated with these screening cells
- Anti-human immunoglobulin is added to the solution which allows briding of red cells that are coated with IgG
- This results in the formation of a visible clump
- This is a group and screen
What labels are included on issued blood?
ABO and RhD status
Other Rh antigens and K
Which patient group should receive K negative blood?
Women of childbearing potential
What is a full crossmatch?
- Uses indirect antiglobulin test
- Patients plasma is incubated with DONOR red cells at 37 degrees for 30-40 mins
- Anti-human immunoglobulin is added to allow cross-linking of antibodies
- Formation of a clump would suggest that antibodies against donor red cell antigens are present in the patient’s plasma
Not suitable in emergencies due to because it take 40 minutes
What is an immediate spin?
- Incubate patient’s plasma and donor red cells for 5 mins and spin
- This will only detect ABO incompatibility
- Used in emergency situations
- IgM anti-A or anti-B will bind to donor RBCs, fix complement and lyse cells
What is an electronic crossmatch?
- Also called electronic issue (EI)
- Compatibility is determined by an IT system without physical testing of donor cells against plasma
How it is done now in modern era - quick, requires fewer staff and allows better stock management
How long do red cells survive in storage?
35 days in 4 degrees
