Blood transfusion Flashcards
What are the different blood groups?
Group A: Anti-B antibodies in plasma, A antigens in RBC
Group B: Anti-A antigens in plasma, B antibodies on RBC
Group AB: Non antibodies in plasma, A and B antigens in RBC
Group O: Anti-A and Anti-B antibodies in plasma, no antigen in RBC
How does the ABO blood system work?
People make IgM antibodies to antigen they don’t have
IgM fully activates complement so incompatible blood transfusion can be fatal
How are A and B antigens formed?
A and B antigens on RBC are formed by adding one or more sugar residues to a common glycoprotein and fructose stem (H antigen) on the red cell membrane
Group O has the H stem only
What genes determine antigens on RBCs?
People with gene for A antigen have an enzyme that adds N-acetylgalactosamine to common H antigen (AA or OA)
People with gene for B antigen have enzyme which adds galactose to common H antigen (BB or OB)
Which antigens are dominant or recessive?
A and B are codominant
O is recessive
O RBCs have no antigens on them so make them a universal donor
Group AB have no antibodies in plasma so makes them a universal acceptor
How do we test the compatibility of blood for transfusion?
In a lab mix sample of blood from patient and donor blood
If incompatible cells will clump together (agglutination)
What are other red cell antigens?
C, c, e, kell, duffy, kidd
What is the most important antigen in the Rhesus system?
D antigen
RhD positive = have D antigen
What are the genes for RhD group?
D gene codes for the D antigen- its dominant
d gene codes for no antigens- recessive
Rhesus positive is DD or Dd
can people without the RhD antigen make anti-D antibodies?
They can make anti-d antibodies (IgG) after exposure to RhD antigen- either by transfusion of RhD positive blood or in women pregnant with a RhD positive fetus
What are implications of anti-D antibodies?
- Future transfusion- patient must in future have RhD negative blood (otherwise could have delayed haemolytic transfusion reaction if given RhD positive blood)
- Haemolytic disease of newborn (HDN)- if RhD negative mother has anti-D then in next pregnancy if the fetus is RhD positive the mother’s IgG antibodies can cross the placenta, attach to the RhD positive RBCs of fetus and cause haemolysis
- if severe: can cause fetus death
- if less severe: baby survives but after birth have high bilirubin levels which can cause brain damage or death
Why is antibody screen performed?
Performed to exclude any clinically significant immune antibodies
How is an antibody screening performed?
Patient’s plasma is incubated with 2 or 3 different fully typed ‘screening’ red cells which are known to possess all the blood group antigens which clinically matter
If antibody screen is negative any donor blood which is ABO or RhD compatible can be given
If antibody screen is positive antibody must be must be identified with use of large panel of red cells
Donor units of blood that lack corresponding blood group antigen are then chosen for cross matching with recipients plasma prior to transfusion
What compatibility tests are used?
- Patient’s blood sample
- ABO group: test patient’s red cells with known anti-A and anti-b reagents
- RhD group: test patient’s red cells with known anti-D reagent
- select donor blood of same ABO and RhD group
- Use antibody screen test to identify antibodies - Cross- Match
- Patient’s serum mixed with chosen donor red cells- should not react, if it does react its incompatible
What is the criteria for blood donors?
Blood is taken from volunteers and unpaid donors
Aged 17-70
Donor’s are excluded if they have any disease which makes blood donation hazardous for them e.g. neurological or cardiovascular
Donor’s excluded if blood is hazardous for recipient e.g. risk of infection or drugs
What tests are undertaken for blood donations?
Group screening
-Every blood group has ABO and RhD group determined as well as other groups e.g. C, c, E, e and K
Every donation is tested to ensure there is no clinically significant red cell antibodies are present in plasma
What infections are tested for in donor blood and what tests are done?
HIV: ant-HIV 1+2 Ab: PCR Hep B: HBsAG; PCR Hep C: anti-HCV Ab: PCR Hep E: PCR HTLV: anti- HTLV Ab Syphilis: TPHA (Ab test)
Also for some:
CMV (cytomegalovirus): anti-CMV Ab
T.Cruzii: anti-T. Cruzii Ab
Malaria: Anti- malarial Ab
What is the significance of CJD?
Creutafeldt-Jacob Disease
Prion disease have been found in membrane of lymphocytes and platelets
Prions of variant CJD have been found in lymphoreticular tissues
There are 4 variant CJD transmitted by transfusion of blood or blood products to humans
A blood test to exclude donors with CJD is not yet available
WBCs are often removed from donor blood
What blood component has all coagulation factors?
Fresh Frozen Plasma (FFP)
Has a 3 year shelf life
Should be left at room temp. 2-30 mins before use then given ASAP
Need to match ABO group to give this to donor
Give to patient if patient is bleeding, had abnormal coagulation or to reverse warfarin effects
What is cryoprecipitate?
Made from FFP
Only has factors VIII, XIII and VWF and fibrinogen
Has a 3 year shelf life
Thaw FFP at 4-8 degrees C overnight
Useful if there’s lots of bleeding and in inherited hypofibrinogenemia
What group of FFP should be given in an emergency?
Group AB FFP should be given- has no antibodies in plasma
If a mother is A neg and her fetus is A pos, can we prevent the mother producing anti-D antibodies?
Yes, give the mother some anti-D antibody
These will coat the baby’s deposited RBCs and can be removed by spleen
Should ‘whole blood’ be used?
donor blood is collected with anti-coagulant
It’s inefficient to use blood containing RBCs, platelets and plasma
Patients should only be treated with the component they require
What are the benefits of component therapy?
Component therapy allows more efficient use of blood donations and less waste of valuable resources
Components are separated by centrifuging a unit of donor blood and squeezing each layer into satellite bags
