Blood transfusion

Question 1

What are the different blood group antigens?

Answer 1

• 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

Question 2

What can stimulate antibody production?

Answer 2

• 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

Question 3

What is agglutination?

Answer 3

• The clumping together of red cells into visible agglutinates by antigen-antibody reactions (not clotting)
• Results from antibody cross-linking with the antigens

Question 4

What can we use agglutination for?

Answer 4

• 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)

Question 5

What is the clinical significance of the ABO system?

Answer 5

• 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

Question 6

Define the ABO groups

Answer 6

• 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

Question 7

How do we test blood groups?

Answer 7

• 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

Question 8

How do you carry out the test?

Answer 8

• 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

Question 9

What is the compatibility in ABO?

Answer 9

Recipient

• O - only receive O
• A - receive O or A
• B - receive O or B
• AB - receive All

Question 10

What is the Rh grouping system?

Answer 10

• 50+ antigens
• most important is D
• People with D Ag are RhD positive (85%)
• Other 4 main Ags are C,c,E,e

Question 11

In what situations is the Rh +/-ve significant?

Answer 11

• 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

Question 12

What causes HDN?

Answer 12

• 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

Question 13

What is RAADP?

Answer 13

• 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

Question 14

Why do we need to antibody screening

Answer 14

• 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

Question 15

How do we identify an antibody?

Answer 15

• Compare the pattern of reactions with each reagent cell of ID panel, with the pattern of antigens on the reagent cells

Question 16

What is zeta potential?

Answer 16

• 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

Question 17

What is the indirect anti-globulin test (IAT)?

Answer 17

• 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

Question 18

What is the immediate spin cross-match (ISX)?

Answer 18

• 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

Question 19

What is full indirect antiglobulin test (IAT) cross match?

Answer 19

• 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

Question 20

How do we check the donated blood?

Answer 20

• 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

Question 21

What is FFP?

Answer 21

• 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

Question 22

How do we store platelets?

Answer 22

• 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

Question 23

What is cryoprecipitate?

Answer 23

Contains FVIII, vWF and fibrinogen

• 2 units usually given together
• monitor fibrinogen levels by clotting screens

Question 24

How do we keep haemovigilance?

Answer 24

• 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