Blood Transfusion

Question 1

What are blood groups derived from?

Answer 1

Each person has genes that encode for antigens on the surface of their red blood cells

A genes code for a certain antigen, B genes for another and O genes are non functional and do not encode an antigen

Blood groups are derived from the genes you have that result in the presence of antigens on your RBCs

Question 2

How does your blood type influence your antibodies towards other blood types?

Answer 2

Blood type A - antibodies against B

Blood type B - antibodies against A

Blood type O - antibodies against A and B

Blood type AB - NO antibodies against A or B

Question 3

What type of antibodies are formed against blood type antigens?

Answer 3

IgM - because they are sugars

Question 4

Why are blood type antibodies described as naturally occurring?

Answer 4

Because usually you only develop antibodies to antigens that you encounter later in life

The ABO antigens are presented by bacteria in the bowel though, and so you have antibodies against them from very early life - even from vertical trnasmission

Question 5

What are the most common blood types in the UK?

Answer 5

A & O

Question 6

Which blood type is the universal donor? Which is the universal recipient?

Answer 6

O is universal donor

AB universal recipient

Question 7

How does transfusion of plasma differ from transfusion of red cells?

Answer 7

If you transfuse red cells you are giving the patient the antigens of whichever blood type they are

If you transfuse plasma you are transfusing the antibodies of whichever blood type the donor has

Universal donor / recipient is switched

Question 8

How does the reaction from an incorrect red cell transfusion compare to an incorrect plasma transfusion?

Answer 8

Transfusing incompatible red cells causes an extremely bad reaction

Transfusing incompatible plasma isn’t as bad

Question 9

What percentage of the population are RhD negative?

Answer 9

Depends on ethnicity, in caucasians about 15%

Question 10

If you are RhD negative and are exposed to RhD antigens what happens? When can this happen?

Answer 10

You will make anti-D antibodies and there will be a severe reaction

Can occur in blood transfusions and pregnancy

Question 11

If a mother is RhD negative and the baby has paternally derived RhD antigens what happens?

Answer 11

Transfusion reactions and possibly haemolytic disease in the newborn

Question 12

What sort of screening is given to those who become blood donors?

Answer 12

Behavioural screening: age, travel, sex history, tattoos

Blood group and RhD screening

Hepatitis / HIV / Syphilis testing

Question 13

What are some indications for red cell transfusion?

Answer 13

1. Correction of severe acute anaemia
2. Improve QOL of patient with chronic anaemia
3. Prepare a patient for surgery or speed up recovery
4. Reverse damage caused by patients own sickle cells

Question 14

How much will 1 unit of blood (from one donor) increase the haemoglobin in a recipient?

Answer 14

Increases haemoglobin by about 5 g/L

Question 15

What is apheresis donation?

Answer 15

Donor is attached to a machine for 1 or 2 hours and the machine can extract certain components of blood

eg. it takes 4 blood donors to get 1 dose of platelets, but only 1 apheresis donor to get the same dose

Question 16

What temperature are RBCs stored and and over how long are they transfused? Platelets?

Answer 16

RBCs - stored at 4 degrees, transfused over 2-3 hours

Platelets - stored at 22 degrees, transfused over 20-30 minutes

Question 17

What are some indications for platelet transfusion?

Answer 17

Massive haemorrhage

Bone marrow defects

Prophylaxis for surgery

Cardiopulmonary bypass

Question 18

What are the different types of plasma that are transfused?

Answer 18

FFP - fresh frozen plasma. stored frozen, needs 20-30 mins to thaw

Cryoprecipitate - basically a fibrinogen concentrate. stored frozen and needs 20 mins to thaw

Question 19

What does the coombs test test for?

Answer 19

detects the presence of antibodies or complement proteins on the surface of RBCs

Important test for autoimmune haemolytic anaemia

Question 20

What sort of antibodies are produced against RhD in RhD negative people? Why is this important?

Answer 20

IgG because RhD is a protein

Because IgG antobodies cross the placenta

Question 21

If an RhD negative mother has had an RhD positive baby what does this mean?

Answer 21

In subsequent pregnancies the anti-D antibodies can cross the placenta

Question 22

When maternal anti D antibodies cross into the fetal circulation what happens?

Answer 22

Haemolytic disease of the newborn

Results in the baby becoming profoundly anaemic and possibly developing cardiac failure and possibly dying

Question 23

Is RhD the only antigen that causes haemolytic disease of the newborn?

Answer 23

No

Other Rh antigens and ABO etc may cause it

Profound in RhD though due to the immunogenicity of the antigen

Question 24

How has the prevalence of haemolytic disease of newborns (HDN) been drastically reduced?

Answer 24

Due to administration of anti-D around the time of birth in RhD negative mothers

Induces tolerance in the mother and prevents the development of RhD antibodies

Question 25

When is anti-D completely necessary throughout the course of pregnancy?

Answer 25

When the mother has had a sensitizing event such as trauma or haemorrhage that has caused the development of RhD antibodies