Blood Transfusion Flashcards
Why is blood a scarce resource?
- so far it cannot be synthesised
- scarce resource because 1 donor can give about 1 pint every 4 months
- need 9,000 units per day in the UK
- can’t stockpile, blood shelf life is about 5w
-> use carefully
When would you give a patient a blood transfusion?
- in major blood loss when fluids would not be enough
- in anaemia when b12, folate or iron are not appropriate
-> Doctor’s decision
Who discovered ABO blood groups?
Landsteiner 1901 (Nobel prize winner) - early human blood transfusions were fatal
What do genes that determine ABO group encode?
- A gene codes for enzyme which adds N-acetyl galactosamine to common glycoprotein and fucose stem
- B gene codes for enzyme which adds galactose
Inheritance pattern of ABO genes
- 0 is recessive
- A and B are co-dominant
What is the molecular structure of the different blood types?
- O: only H stem
- A: H stem with A sugar added onto it
- B: H stem with B sugar (galactose) added onto it
- AB: there are A and B
What are the antibodies that cause adverse reactions when you are given the wrong blood type?
- IgM antibodies, present from birth (=naturally occurring)
- they fully activate the complement cascade and cause haemolysis of RBCs -> often fatal
- You have the ones against the RBC antigen that you don’t have.
what is the most and least common blood group in the UK?
Most: 0 (47%)
Least: AB (3%)
A has 42% and B has 8%
How do you check if you the donor matches the patients?
- now usually done with machines
- test with known anti-A and anti-B reagents
- also x-match the donor’s blood with the pateints serum to check for agglutination
What fraction of people are RhD positive/negative?
85% are positive
15% are negative
What is an immunological difference between ABO and RhD antibodies?
the antibodies for ABO are naturally occurring (from birth) and make IgM pentamers.
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. (-> can cross the placenta)
What is the reaction if you give the wring RhD?
Delayed haemolytic transfusion reaction because they are IgG type antibodies, they can’t activate the whole compliment system
- There are AB coated RBCs, macrophages in the spleen attack them -> Hb can cause renal failure, you get jaundice etc
- NOT IMMIDIATE FATAL REACTION LIKE WITH IgM !!!
What are implications of anti-D antibodies?
- 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) - 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
What fraction of donors actually have O neg?
6-7%
What are some antigens aside from ABO and RhD?
- Don’t routinely match blood for all these, eg Rh group -C, c, E, e; others - Kell, Duffy, Kidd, etc
- About 8% of pts transfused will form Ab to one or more of these antigens
- Once have formed antibody must use corresponding antigen negative blood; or else risk of delayed haemolytic reaction (can be severe)
How do we know if a 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 are blood components?
- you no longer routinely give whole blood to patients
- you give components that they need
Why do you no longer give whole blood to patients?
- more efficient; less waste as patients don’t need all the ‘components’; - some components degenerate quickly if stored as ‘whole blood’ - avoid fluid overload
How is donor blood separated into different components?
Split one unit of blood by centrifuging whole bag (red cells bottom, platelets middle, plasma top) then squeeze each layer into satellite bags and cut free (closed system)
Transfusion of RBCs
- 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 (lose 1/3 of the cells, only do this when there are strong indications)
FFP
= fresh frozen plasma
- 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 or now even 3 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
- you can now leave it in the fridge for 1h (special indications only)
What are indications for 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
or if surgeons are about to make them bleed
NB not just to replace volume/ fluid loss
What three main categories of products are won from a blood transfusion?
- RBCs
- Platelets
- Plasma (FFP, cryoprecipitate, plasma for fractionation (not in the UK) - albumin, factors etc)
Cryoprecipitate?
- From frozen plasma thawed at 4-8oC overnight residue remains
- Contains fibrinogen and factor VIII
- Same as FFP - store at -30oC for 2 yrs
- Standard dose = from 10 donors (5 in a pack)
Indications:
- If massive bleeding and fibrinogen very low
- Rarely hypofibrinogenaemia
