Blood Transfusion 1 Flashcards
What is RhD positive?
85% of population
Carry the RhD antigen
Patients can receive RhD negative (just a waste!) or RhD positive red cells
What is RDh negative?
15% of population
Lack the RhD antigen
Patients can make immune anti-D if exposed to RhD positive red cells
What are immune anti-D antibodies?
Are IgG (so cross the placenta)
Do not cause direct agglutination of RBCs
Cause delayed haemolytic transfusion reaction.
There are some other Rh antigens e.g., C, c, E and e
What are other blood groups antigens?
Kell (K), M, N, S, Duffy (Fy), Kidd (Jk)
But we only match for these if patient has corresponding antibody (or occasionally in certain other situations)
Who can RhD negative cells be given to?
Can safely be given to anyone, but often in short supply. Occasionally (emergency/shortage) it may be necessary to use RhD-positive blood for the transfusion of RhD-negative patients, this does not cause acute problems but will sometimes induces formation of anti-D.
Will be picked up by the lab next time they need blood. RhD negative blood would then be issued. RhD negative women exposed to RhD positive blood can produce immune anti-D, which can cause haemolytic disease of the newborn or severe foetal anaemia and heart-failure (hydrops fetalis) in pregnancy.
What are the immune antibodies involved in blood transfusion?
IgG
What is antibody screening and what is screened?
Can’t test all other RBC antigens (100s) but about 1-3% of patients have immune RBC antibodies to one or more RBC antigen, As a result of TRANSFUSION and/or PREGNANCY.
REALLY IMPORTANT to identify clinically significant RBC antibodies and transfuse RBCs that are negative for that antigen yo prevent a DELAYED HAEMOLYTIC TRANSFUSION REACTION.
How does antibody screening occur?
Use 2 or 3 reagent red cells containing all the important red cell antigens between them. Screen by incubating the patient’s plasma and screening cells using IAT technique.
What is the IAT technique?
Indirect antiglobulin technique.
Bridges red cells coated by IgG, which can’t themselves bridge 2 red cells – to form a visible clump. Takes 30 mins’ incubation at 37°C.
Why does antibody screening happen before every transfusion even if it might have been done before?
Because new antibodies can be made after a transfusion or in pregnancy.
What is electronic issue?
Electronic issue (EI) is the selection and issue of red cell units where compatibility is determined by IT system, without physical testing of donor cells against patient plasma.
What are the advantages of electronic issue?
Quicker
Fewer staff
No need to have blood “standing by” just in case
Remote issue
Better stock management
What is serological crossmatch and how it’s done?
Full crossmatch:
Indirect antiglobulin technique: Patient plasma incubated with donor red cells at 37C for 30-40 mins, will pick up antibody antigen reaction that could destroy the red cells and cause extravascular haemolysis. Add antiglobulin reagent (AHG). IgG antibodies can bind to RBC antigens but do not crosslink so AHG reagent is added.
Immediate spin: Saline, room temperature. Incubate patient plasma and donor red cells for 5 minutes only and spin, will detect ABO incompatibility only. IgM anti-A and/or anti-B bind to RBCs, fix complement and lyse the cell.
What are donor RBCs labelled with?
ABO and D type
Kell
Other Rh antigens
What are the three pillars of patient blood management?
Optimise haemopoiesis
Minimise blood loss and bleeding
Harness and optimise physiological tolerance of anaemia