Haem 11 - Blood transfusion Flashcards
Where is blood obtained from?
Humans - 1 donor gives approx 1 pint (unit) - max. every 4 months
Need 9,000 units of blood/day in U.K. (can’t stockpile - blood shelf life = 5 weeks)
When would you use blood?
If massive bleeding - if ‘plain fluids’ not sufficient
If anaemic - if iron/ B12/ folate not appropriate
Describe the different blood groups?
ABO blood groups
A and B antigens on red cells formed by adding one or other sugar residue onto a common glycoprotein and fructose stem on red cell membrane.
A = galnac (N-Acetylgalactosamine)
B = gal (galactose)
Group O has no A or B sugars - stem only
What determines the different antigens for blood groups?
A gene - codes for enzyme which adds N-acetyl galactosamine to common glycoprotein and fucose stem
B gene - codes for enzyme which adds galactose
The A and B genes are co-dominant
O gene - is recessive. E.g if a person is group A; genes could be AO or AA
Describe what blood antibodies people have?
Person has antibodies against any antigen NOT present on own red cells
This antigens are naturally occurring nearly from birth - IgM
Describe the IgM antibody
it is a ‘complete’ antibody, so:- fully activates complement cascade to cause haemolysis of red cells
What happens in a patient who has received an ABO incompatible transfusion, where patient has the corresponding antibody.
E.g blood group A given to patient who is group O - so has anti-A and anti-B) - then antibody/ antigen interaction often fatal.
In laboratory tests, IgM Antibodies interact with corresponding antigen 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
You must give transfusions to people with the same group
Draw the table for ABO blood groups
See table/see slides
What are RhD groups?
RhD groups are the most important:
RhD positive if they have D antigen
Rhd negative if they do not have D antigen
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
85% of people are RhD positive; 15% are RhD negative
What happens in people who lack the RhD antigen?
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
See table
What are the 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
It is important to avoid RhD negative patients from making anti-D antibodies
O negative is used an emergency blood when patients blood group is not known
What are the other antigens present on red cells?
Don’t routinely match blood for all these, eg Rh group -C, c, E, e; others - Kell, Duffy, Kidd, etc
About 8% of pints transfused will form antibodies 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 is 1 unit of blood collected in?
Bag containing anticoagulant.
No longer routinely give whole blood to patients - use parts needed:
more efficient; less waste as patients don’t
need all the ‘components’;
some components degenerate quickly if
stored as ‘whole blood’
Red cells – concentrated, as plasma
removed; also avoids fluid overloading patients
How is a unit of blood separated into its 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)
