Blood transfusion Flashcards
1
Q
What are the different blood group antigens?
A
- 26 known blood group systems
- ABO and Rh are clinically most important
- Antigens in transfused blood can stimulate a patient an Ab but only if the patient lacks the Ag themselves
- The frequency of Ab production is very low but increases the more transfusion that are given
2
Q
What can stimulate antibody production?
A
- Blood transfusion - blood carrying Ags foreign to the patient
- Pregnancy - foetal antigen entering maternal circulation during pregnancy or at birth
- Environmental factors - naturally acquired e.g anti-A and anti-B
3
Q
What is agglutination?
A
- The clumping together of red cells into visible agglutinates by antigen-antibody reactions (not clotting)
- Results from antibody cross-linking with the antigens
4
Q
What can we use agglutination for?
A
- Ag-Ab reaction is specific so can identify the presence of a red cell antigen (blood group), or the presence of an Ab in the plasma (Ab screening/identification)
5
Q
What is the clinical significance of the ABO system?
A
- A and B antigens are very common (55%)
- Anti-A, anti-B or anti-AB Abs are bery common (97%)
- High risk of A or B cells being transfused in someone with the Ab in a random situation
- ABO Abs can activate complement causing intravascular haemolysis
6
Q
Define the ABO groups
A
- Group A = A cells, with A Ags and anti-B Abs
- Group B = B Ags and anti-A Abs
- Group AB = no Abs and A and B Ags
- Group O = Anti-A and anti-B antibodies, but no antigens
7
Q
How do we test blood groups?
A
- Test pts red cells with anti-A, anti-B and anti-D
- agglutination shows that a particular antigen is on the red cells
- no agglutinaton shows absence of the antigen
- Test plasma with A cells and B cells
- agglutination shows that a particular antibody is present
- no agglutination shows the antibody is absent
8
Q
How do you carry out the test?
A
- Get a card that has a gel impregnated with an antibody (a,b,d)
- D is from the Rh grouping system
- put the red cells from the pt on top, spin it in the incubator
- If there is agglutination, they wont be able to pass through the gel matrix and so sit on top
- Forwards test = look for Ags on red cells
- Reverse test = antibodies in the plasma
9
Q
What is the compatibility in ABO?
A
Recipient
- O - only receive O
- A - receive O or A
- B - receive O or B
- AB - receive All
10
Q
What is the Rh grouping system?
A
- 50+ antigens
- most important is D
- People with D Ag are RhD positive (85%)
- Other 4 main Ags are C,c,E,e
11
Q
In what situations is the Rh +/-ve significant?
A
- Transfusion - D ag is very immunogenic and anti-D is easily stimulated; all Rh abs can cause severe transfusion reaction
- Pregnancy - Rh antibodies are usually IgG and can cause haemolytic disease of the newborn; anti-D is still most common severe cause of HDN
12
Q
What causes HDN?
A
- Rh+ father
- Rh- mother carrying her first Rh+ foetus. Rh ags from the developing foetus can enter the mother’s blood during delivery
- In response to the foetal Rh ags, the mother will produce anti-Rh abs
- If the woman becomes pregnant with another Rh+ foetus, her anti-Rh abs will cross the placenta and damage foetal RBCs
13
Q
What is RAADP?
A
- Routine antenatal anti-D prophylaxis
- An injection of anti-D will bind to remove any foetal RhD+ red cells in circulation - want to remove the non-self ag so that the mother doesnt produce the reaction
- Anti-D is also given after any event that may cause a foeto-maternal haemorrhage (bleed between mum and foetus) - eg. abdominal trauma, intrauterine death, sponateous or therapeutic abortion
14
Q
Why do we need to antibody screening
A
- Other clinically significant antibodies that can cause a haemolytic transfusion reaction
- Need to screen so that if there is any detected, we can provide antigen negative blood to avoid immune reaction
- Patient’s serum is mixed with 3 selected screening cells, incubated for 15 mins at 37 and then centrifuged for 5 mins
15
Q
How do we identify an antibody?
A
- Compare the pattern of reactions with each reagent cell of ID panel, with the pattern of antigens on the reagent cells
16
Q
What is zeta potential?
A
- Red cells have a positively charged ionic cloud around them
- IgM Abs can span the gap between RBCs
- IgG cannot, because they are too small to overcome the zeta potential
- Low ionic strength saline (LISS) is negatively charged so neutralises the positive Zeta potential
- IgG can now span the gap
17
Q
What is the indirect anti-globulin test (IAT)?
A
- Used to detect IgG
- LISS counteracts zeta potential
- Results in agglutination
- Used for screening for Abs; identifying abs; and cross-matching donor blood with recipient plasma where there are known abs or a previous history of abs
18
Q
What is the immediate spin cross-match (ISX)?
A
- Ab screen is -ve
- Checking donor red cells against patient’s plasma - ABO check, incubate 2-5 mins (room temp), spin and read
- Checking ABO, so IgM, so no problem with z potential
19
Q
What is full indirect antiglobulin test (IAT) cross match?
A
- Ab screen positive or patient has known ab history
- Select ag negative donor red cells and incubate with patient serum for 15 mins a t body temp
20
Q
How do we check the donated blood?
A
- Donor selection - questionnaire - lifestlye, health, not previously transfused
- Collection procedure - arm cleaning/ diversion pouch
- Comprehensive testing of all products - HIV, hep B,C, syphilis, HTLV, bacteria in plateltes
21
Q
What is FFP?
A
- Fresh frozen plasma
- contains all clotting factors
- given for coagulopathy with associated bleeding
- Requires clotting screens to monitor
- only has 24 hr life after thawing
22
Q
How do we store platelets?
A
- Adult pool of platelets from 4 donors (suspended in plasma from 1 donor)
- 60% of doses are apheresis units
- Platelets required to create clots to reduce bleeding
- Some drugs given to reduce efficacy of platelets, so pt history imprtant
23
Q
What is cryoprecipitate?
A
Contains FVIII, vWF and fibrinogen
- 2 units usually given together
- monitor fibrinogen levels by clotting screens
24
Q
How do we keep haemovigilance?
A
- Serious hazards of transfusion (SHOT) - voluntary reporting, report all serious adverse events (SAE) and serious adverse reactions (SAR)
- Serious adverse blood reactions and events (SABRE) - mandatory reporting, report all SAR and SAE where the root cause error was the QC system
