Blood transfusion

Question 1

when do you use blood for blood transfusions?

Answer 1

Balance between benefits vs risks ie: when no safer alternative available eg:
If massive bleeding - if ‘plain fluids’ not sufficient
If anaemic - if iron/ B12/ folate not appropriate

Doctor’s decision: has to prescribe

Question 2

what do the ABO blood groups mean?

Answer 2

Most important of all blood groups
A and B antigens on red cells formed by adding one or other sugar residue onto a common glycoprotein and fucose stem on red cell membrane
Group O has neither A or B sugars - stem only

Question 3

what are the genes for the ABO blood group?

Answer 3

Antigens determined by corresponding genes
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 4

ABO group antigens and antibodies- how does that work?

Answer 4

Person has antibodies against any antigen NOT present on own red cells

Question 5

what is the naturally occurring antibody?

Answer 5

it is a ‘complete’ antibody, so:- fully activates complement cascade to cause haemolysis of red cells
In laboratory tests, IgM Abs interact with corresponding ag to cause agglutination eg: if patient is group B, he has anti-A antibody in plasma - when add to group A cells - agglutination seen (clump) - shows cells are incompatible

Question 6

Blood group A

• antigens on RBC?
• antibodies in plasma?

Answer 6

• antigens on RBC = A

- antibodies in plasma = anti-B

Question 7

Blood group O

• antigens on RBC?
• antibodies in plasma?

Answer 7

• antigens on RBC =nil

- antibodies in plasma = anti-A, anti-B

Question 8

how do you pick the right blood to give?

Answer 8

Patient blood sample (plasma + cells)
ABO group (test with known anti-A and anti-B reagents)
Select donor unit of same group (ag matter)
X-match: patient’s serum mixed with donor red cells - should not react: if reacts (agglutinates) = incompatible

Question 9

Which RH antigen group is more important?

Answer 9

RhD

Question 10

what are the RhD groups?

Answer 10

Blood groups: RhD positive (if have D antigen) or RhD negative (if not)

Question 11

what are the genes for RhD groups?

Answer 11

D - codes for D antigen on red cell membrane
d - codes for no antigen and is recessive

Therefore
dd = no D antigen = RhD negative
DD or Dd = D antigen present = RhD positive

Question 12

can people who mae antibodies make anti-d antibodies after exposure?

Answer 12

People who lack the RhD antigen (ie: RhD negative) CAN make anti-D antibodies AFTER they are exposed to the RhD antigen - either by transfusion of RhD positive blood or in women, if they are pregnant with an RhD positive fetus
Anti-D antibodies are IgG antibodies

Question 13

RhD positive

• antigens on RBC?
• antibodies in plasma?

Answer 13

RhD positive

• antigens on RBC = D positive
• antibodies in plasma = nil

Question 14

RhD negative

• antigens on RBC?
• antibodies in plasma?

Answer 14

• antigens on RBC = nil

- antibodies in plasma = can make anti-D if sensitised

Question 15

what are the implications of anti-D antibodies and further transfusions?

Answer 15

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)

RhD GROUP - IMPORTANCE = avoid Rh D neg patients making anti-D

Question 16

what blood can rhd positive patients get?

Answer 16

hen it comes to blood transfusion, anyone who is Rh positive can receive blood from someone who is Rh negative, but those with negative blood types cannot receive from anyone with a positive blood type.

Question 17

How do we know if patient will need antigen negative blood?

Answer 17

BEFORE each transfusion episode, test patient’s blood sample for red cell antibodies
Therefore, before transfusing patient, as well as testing their ABO and RhD group, must do an ‘antibody screen’ of their plasma

Question 18

what can whole blood be split into?

Answer 18

red cells
platelets
plasma

Question 19

describe red cells collected for transfusion

Answer 19

1 unit from 1 donor - ‘packed cells’ (fluid plasma removed)
Shelf life 5 weeks; stored at 4oC (fridge)
Give through a ‘blood giving set’ - has filter to remove clumps/debris
Rarely need frozen red cells (National Frozen Bank) - for rare groups/ antibodies - poor recovery on thawing

Question 20

describe FFP

Answer 20

1 unit from 1 donor (300ml) can get small packs for children
Stored at -30oC (frozen within 6h of donation to preserve coag factors)
Shelf life 2 years
Must thaw approx 20-30 mins before use (if too hot, proteins cook)
Give ASAP – ideally within 1h or else coag factors degenerate at room temp
Dose 12-15ml/kg = usually 3 units
Need to know blood group - no x-match, just choose same group (as contains ABO antibodies, which could cause a bit of haemolysis

Question 21

indications of FFP?

Answer 21

1. If bleeding + abnormal coag test results (PT, APTT)
   
   • Monitor response - clinically and by coag tests
2. Reversal of warfarin (anticoagulant) eg for urgent surgery (if PCC not available)
3. Other conditions occasionally

NB not just to replace volume/ fluid loss

Question 22

describe cryoprecipitate

Answer 22

From frozen plasma thawed at 4-8oC overnight residue

Question 23

describe platelet donation

Answer 23

1 pool from 4 donors (= standard adult dose) or from 1 donor by apheresis (cell separator machine)
Store at 22oC (Room temp) - constantly agitated
Shelf life 5 days only - (risk of bacterial infection)
Need to know blood group

Question 24

does platelet donation need cross match?

Answer 24

No cross-match, just choose same group (as platelets have low levels of ABO antigens on, so wrong group platelets would be destroyed quickly) - and can cause RhD sensitisation, as some red cell contamination

Question 25

platelets indications

Answer 25

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 26

what are fractionated products?

Answer 26

Fractionated (like oil)
Factor VIII and IX
For haemophilia A and B respectively (males)
Factor VIII for von Willebrand’s disease
Heat treated - viral inactivation
Recombinant factor VIII or IX alternatives increasingly used, but expensive
Immunoglobulins
IM: Specific - tetanus; anti-D; rabies
IM: Normal globulin - broad mix in population (eg: HAV)
IVIg – pre-op in patients with ITP or AIHA

Albumin
4.5%
Useful in burns, plasma exchanges, etc
Probably overused (not indicated in malnutrition)
20% (salt poor)
For certain severe liver and kidney conditions only