Blood transfusion Flashcards
(26 cards)
when do you use blood for blood transfusions?
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
what do the ABO blood groups mean?
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
what are the genes for the ABO blood group?
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
ABO group antigens and antibodies- how does that work?
Person has antibodies against any antigen NOT present on own red cells
what is the naturally occurring antibody?
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
Blood group A
- antigens on RBC?
- antibodies in plasma?
- antigens on RBC = A
- antibodies in plasma = anti-B
Blood group O
- antigens on RBC?
- antibodies in plasma?
- antigens on RBC =nil
- antibodies in plasma = anti-A, anti-B
how do you pick the right blood to give?
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
Which RH antigen group is more important?
RhD
what are the RhD groups?
Blood groups: RhD positive (if have D antigen) or RhD negative (if not)
what are the genes for RhD groups?
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
can people who mae antibodies make anti-d antibodies after exposure?
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
RhD positive
- antigens on RBC?
- antibodies in plasma?
RhD positive
- antigens on RBC = D positive
- antibodies in plasma = nil
RhD negative
- antigens on RBC?
- antibodies in plasma?
- antigens on RBC = nil
- antibodies in plasma = can make anti-D if sensitised
what are the implications of anti-D antibodies and further transfusions?
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
what blood can rhd positive patients get?
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.
How do we know if patient will need antigen negative blood?
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
what can whole blood be split into?
red cells
platelets
plasma
describe red cells collected for transfusion
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
describe FFP
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
indications of FFP?
- If bleeding + abnormal coag test results (PT, APTT)
- Monitor response - clinically and by coag tests
- Reversal of warfarin (anticoagulant) eg for urgent surgery (if PCC not available)
- Other conditions occasionally
NB not just to replace volume/ fluid loss
describe cryoprecipitate
From frozen plasma thawed at 4-8oC overnight residue
describe platelet donation
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
does platelet donation need cross match?
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
