Blood Transfusion Flashcards
what makes a blood group a specific blood group?
presence or absence of antigens on surface of red cell membrane
what defines type of antibodies on red cell membrane?
inherited from both parents
blood grouping system?
ABO system
types of blood group?
A (2nd most common)
B (3rd most common)
AB (least common)
O (most common)
which antibodies are present in the plasma in people with each blood type?
A = anti-B antibodies B = anti-A antibodies AB = neither O = anti-A and anti-B antibodies
what happens if someone someone is given wrong blood type?
acute haemolytic transfusion reaction
i.e person with group A is given group B blood > group B blood contains anti-A antibodies which will attack A antigens on patients own RBCs causing lysis of the RBCs
which blood groups can donate to each other?
O can donate to anyone (as they have no antigens on surface) but can only receive from group O as group O blood contains both anti-A and anti-B antibodies
group A can donate to A and AB (as they have only A antigens) but can only receive from group A or O (as group B has anti-A antibodies)
group B can donate to B and AB but can only receive from B and O
group AB can only donate to AB (as group A has anti-B, group B has anti-A and group O has both) and can receive from all groups (as AB blood contains no antibodies)
another blood grouping system>
rhesus (RhD antigen)
describe RhD antigen?
inherited antigen composed of 2 alleles (D and d - d is recessive) very immunogenic (exposure to tiny bit of D antigen causes reaction forming anti-D antibodies)
rhesus +ve vs -ve genotype?
\+ve = DD or Dd -ve = dd
why is formation of anti-D antobodies harmful?
can cause problems with blood transfusions in the future causing a transfusion reaction
anti-D antibodies can cross the placenta in pregnant women causing haemolytic disease of the newborn if rhesus -ve mum is carrying rhesus +ve baby
other families of RBC antigens aside from ABO and RhD are usually less immunogenic, what does this mean?
less likely to form antibodies if exposed to something
but may still form antibodies when exposed to foreign RBC antigens
when might someone be exposed to foreign RBC antigens?
pregnancy (exposed to foetal blood during haemorrhage etc)
transfusion
antibodies formed in response to foreign antigen tend to be which type?
IgG rather than IgM meaning that the haemolytic transfusion reaction is more delayed
what is blood tested for when a sample is sent before a blood transfusion?
ABO and RhD group
antibody screen
can be done via electronic crossmatch (if antibody screen in -ve) or wet crossmatch (where donor red cells mixed with sample of patient plasma if patient blood sample contains antibodies)
risks of transfusion?
infection (bacterial, viral, prion etc)
acute reaction
fluid overload
questions to ask self before giving transfusion?
cause of anaemia if giving for anaemia
think whether anaemia is symptomatic (usually not needed if asymptomatic)
any other medical problems?
restrictive transfusion threshold?
NICE threshold for giving RBC transfusion which advises to only give it if Hb <70, aiming for Hb 70-90
deemed safe in people with normal bone marrow
alternatives to transfusion?
replace iron/B12/folate
minimise blood loss (tranexamic acid (antifibrinolytic) for example)
intraoperative cell salvage plus reinfusion
what is irradiated blood?
blood which has been exposed to irradiation which kills viable donor lymphocytes present in blood component to prevent transfusion associated graft vs host disease (GVHD)
when does GVHD happen?
when the lymphocytes present in the blood which is transfused engraft into the patients bone marrow and start basically making an immune system which fights against the patients own tissues
usually only occurs in people who are immunosuppressed but is universally fatal
who should receive irradiated blood?
immunosuppressed
people who have been treated with purine analogue chemotherapy
people who have undergone autologous or allogenic stem cell transplant (only require irradiated blood short term)
what is CMV -ve blood?
blood which has been specifically irradicated of cmv (only a very small risk of CMV transmission in normal blood components)
when is CMV -ve blood used?
for people who would be at risk of harm if they contracted CMV
e.g pregnant women (can cross placenta and cause foetal morbidity), neonates
