BLOOD TRANSFUSION

Question 1

what determines your blood group?

Answer 1

antigens determined by corresponding genes A, B and O

A gene codes for enzyme which adds N-acetyl galactosamine to common glycoprotein and fucose stem
B gene codes for enzyme which adds galactose
A and B genes are co-dominant
O gene is ‘recessive’
eg: person is blood group A - genes could be AA or OA

Question 2

what determines whether you are RhD positive or negative?

Answer 2

D gene codes for D antigen on red cell membrane –> RhD positive

d gene codes for no antigen and is recessive –>RhD negative

Question 3

what are the implications of anti-D antibodies?

Answer 3

1. Future transfusions
   
   • patient must, in future, have RhD neg blood (otherwise his anti-D would react with RhD pos blood - causes delayed haemolytic transfusion reaction - anaemia; high bilirubin; jaundice etc)
2. HDN = haemolytic disease of the newborn
   
   • if RhD neg mother has anti-D - and in next pregnancy, fetus is RhD pos - mother’s IgG anti-D antibodies can cross placenta - causes haemolysis of fetal red cells - if severe: hydrops fetalis; death

Question 4

if someone is group B what antigens and antibodies so they have?

Answer 4

antigen B

anti- A antibody

Question 5

why can group O blood be given to everyone?

Answer 5

it contains no antigens

Question 6

why do we split a blood donation into its different components?

Answer 6

more efficient
patient might not need all component s

some components degenerate quickly if stored as ‘whole blood’

prevents fluid overloading

Question 7

why use fresh frozen plasma?

Answer 7

if they have an abnormal coagulation test result and they are bleeding

if patients are on anticoagulants to prevent clotting

Question 8

when would you use cryoprecipitate?

Answer 8

from frozen plasma

if massive bleeding and fibrinogen v low

Question 9

when would you give platelets?

Answer 9

Mostly haematology patients with bone marrow failure (if platelets <10 x 109/L)

Massive bleeding or acute DIC

If very low platelets and patient needs surgery

If for cardiac bypass and patient on anti-platelet drugs

1 pool is usually enough - rarely need more

Generally, platelets and FFP overused in past - limited resource and cost

Question 10

what must the donors blood be tested for and how are they each tested?

Answer 10

Hepatitis B - HBsAg,
PCR

Hepatitis C - anti-HCV,
PCR

HIV - anti-HIV, PCR

HTLV - anti HTLV

Syphilis - TPHA (spirochete)

Hepatitis E - PCR

Some also tested for CMV (virus)