Blood transfusion

Question 1

What are the different blood groups?

Answer 1

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

Question 2

How does the ABO blood system work?

Answer 2

People make IgM antibodies to antigen they don’t have

IgM fully activates complement so incompatible blood transfusion can be fatal

Question 3

How are A and B antigens formed?

Answer 3

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

Question 4

What genes determine antigens on RBCs?

Answer 4

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)

Question 5

Which antigens are dominant or recessive?

Answer 5

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

Question 6

How do we test the compatibility of blood for transfusion?

Answer 6

In a lab mix sample of blood from patient and donor blood

If incompatible cells will clump together (agglutination)

Question 7

What are other red cell antigens?

Answer 7

C, c, e, kell, duffy, kidd

Question 8

What is the most important antigen in the Rhesus system?

Answer 8

D antigen

RhD positive = have D antigen

Question 9

What are the genes for RhD group?

Answer 9

D gene codes for the D antigen- its dominant
d gene codes for no antigens- recessive
Rhesus positive is DD or Dd

Question 10

can people without the RhD antigen make anti-D antibodies?

Answer 10

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

Question 11

What are implications of anti-D antibodies?

Answer 11

1. Future transfusion- patient must in future have RhD negative blood (otherwise could have delayed haemolytic transfusion reaction if given RhD positive blood)
2. 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

Question 12

Why is antibody screen performed?

Answer 12

Performed to exclude any clinically significant immune antibodies

Question 13

How is an antibody screening performed?

Answer 13

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

Question 14

What compatibility tests are used?

Answer 14

1. 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
2. Cross- Match
   - Patient’s serum mixed with chosen donor red cells- should not react, if it does react its incompatible

Question 15

What is the criteria for blood donors?

Answer 15

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

Question 16

What tests are undertaken for blood donations?

Answer 16

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

Question 17

What infections are tested for in donor blood and what tests are done?

Answer 17

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

Question 18

What is the significance of CJD?

Answer 18

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

Question 19

What blood component has all coagulation factors?

Answer 19

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

Question 20

What is cryoprecipitate?

Answer 20

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

Question 21

What group of FFP should be given in an emergency?

Answer 21

Group AB FFP should be given- has no antibodies in plasma

Question 22

If a mother is A neg and her fetus is A pos, can we prevent the mother producing anti-D antibodies?

Answer 22

Yes, give the mother some anti-D antibody

These will coat the baby’s deposited RBCs and can be removed by spleen

Question 23

Should ‘whole blood’ be used?

Answer 23

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

Question 24

What are the benefits of component therapy?

Answer 24

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