haemostasis 6: blood transfusion Flashcards
what are the major blood groups?
ABO & RhD - A&B antigens on red cells formed by adding N-acetyl galactosamine / galactose sugar residue respectively onto a common glycoprotein and fucose stem on red cell membrane (O has neither A or B sugars - has stem only)
what is the pattern of inheritance for ABO?
A&B co-dominant, O recessive
A&B co-dominant, O recessive
whichever group is not present - IgM antibodies interact with corresponding antigen -> fully activates complement cascade -> haemolysis which is often fatal (in lab tests IgM cause agglutination with Abs - useful for testing blood group)
what is the pattern of inheritance for RhD?
autosomal dominant - D codes for D antigen on red cell membrane (d codes for no antigen) - 85% of people are RhD positive
what happens when RhD- people are given RhD+ blood?
IgG antibodies made - don’t activate whole complement cascade so response less severe than anti-ABabs
what happens if a pregnant woman produces antiRhD antibodies?
abs can cross placenta and cause haemolysis of foetal red cells -> anaemia -> after birth can cross blood-brain barrier and cause death
what other tests need to be done before transfusion re. antibodies in blood?
antibody screen - test patient plasma for other red cell antibodies (present in ~8% of population)
what happens to collected blood?
collected into bag with anticoagulant -> bag centrifuged -> each layer (red cells bottom, platelets middle, plasma top) squeezed into satellite bags -> cut free (closed system to avoid bacteria entering)
what happens to the plasma collected?
converted to: fresh frozen plasma (FFP) / cryoprecipitate - rich concentrated source of fibrinogen + FVIII / fractionation -> albumin / factors etc
how are red cells stored?
in a fridge (shelf life 5 weeks) - rarely frozen as it is less efficient but useful for rarer blood types as lasts longer
how is FFP stored?
frozen (shelf life around 2-3 years) -> thawed for ~30mins at body temp (can’t be heated as proteins will denature)
what are the indications for giving FFP?
- if bleeding + abnormal PT/APTT tests
- reversal of warfarin eg for urgent surgery
how is cryoprecipitate stored?
frozen (made from FFP, shelf life around 2-3 years)
what are the indications for giving cryoprecipitate?
if massive bleeding and fibrinogen v low (genetic hypofibrinogenaemia rare)
how are platelets stored?
room temp & constantly agitated (shelf life 5 days as risk of baterial infection)
