Haem 11 Flashcards
(55 cards)
Where is blood from for donation
Human source - no synthetics yet (research) - not risk free
When is blood used
When no safer alternative
If massive bleeding - if ‘plain fluids’ not sufficient
If anaemic - if iron/ B12/ folate not appropriate
Outline the basis of blood group
All have common H antigen:
A has galnac added on
B has gal added on
AB has some with either, O just has H stem
What are antigens determined by
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
Inheritence of O
It is receissive, so must have 2 O groups if you are blood group O
Possible blood group for A
AA, or OA
Which antibodies do you have against antigens
Person has antibodies against any antigen NOT present on own red cells
What type of antibody is made against the blood cell antigens that you do not have
Naturally occurring (nearly from birth) - IgM: it is a ‘complete’ antibody, so:- fully activates complement cascade to cause haemolysis of red cells
(pentameric so it cross links, activates complemet, and causes MAC and punches holes in the red cell membranes, and cytokine storms)
Group A given to group O patient
blood group A given to patient who is group O - so has anti-A and anti-B - then antibody/ antigen interaction often fatal
What i shown in tests to determine blood group
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
How is ABO blood group determined (slide 9)
Commonest blood group in UK
O, A, B and AB
Which antibodies for each blood group
A: anti B
B: Anti A
O: Anti A and Anti B
AB: none
What is the Cross match
Final check, adding patient’s plasma to the blood you are going to transfuse to ensure it doesnt agglutinate
What types of RH groups
RhD is most important
What are the types of RhD groups
RhD positive or RhD negative
What are the potential genotypes for RhD positive and RhD negative
RhD +ve: DD or Dd
RhD -ve: dd
Most RhD positive in UK
How are antibodies made against RhD in RhD negative people
RhD-ve people 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
What type of antibodies made against RhD antigens
IgG antibodies
What is the consequence of IgG coating of the RhD antien
Not MAC, but complex recognised by spleen, and has membrane pinched out, leading to spherocytes and then are taken out second time around… causes delayed haemolytic transfusion reaction - anaemia; high bilirubin; jaundice etc
Implications of anti-D antibodies (antibodies aginst RhD postiive)
- Future transfusions
- Haemolytic disease of the newborn (HDN)…
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
Why isn’t RhD neg given to RhD positive people
no harm to give RhD neg to a pos patient - just wasteful
What blood group can be used for everyone
O neg used as emergency blood when patient’s blood group not known (NB only 6-7% of donors are O neg)
….
What other antigens can be present on red cells, do they matter
Don’t routinely match blood for all these, eg Rh group -C, c, E, e; others - Kell, Duffy, Kidd, etc
about 8% of patients transfused will form antibody to one or more of these antigens…..
It is important….
Once have formed antibody must use corresponding antigen negative blood; or else risk of delayed haemolytic reaction (can be severe)
What is done to avoid the delayed haemolysis associated with these other antibodues
as well as testing their ABO and RhD group BEFORE each transfusion episode, test patient’s blood sample for red cell antibodies
you need to do a new one each time
