Blood Groups and Blood Transfusion Flashcards
Antigen definition
a protein which can stimulate an immune response
Antibody definition
proteins that are produced by the body in response to the introduction of a foreign antigen
Blood groups definition
a system of antigens in which the antigen specificity is controlled by specific genes
Agglutinate definition
to clump
Agglutinin definition
something that causes clumping
Monoclonal Antibody definition
lab produced and cloned molecules that bind specifically to one epitope (part of the antigen which an antibody recognises)
Patient is blood group A. Will they contain anti-A antibodies in plasma?
No
You don’t produce antibodies to antigens that you have
Blood Group antigens are present on the surface of
- red blood cells
- sometimes platelets and other
body tissues (ABO)
Blood Group Antigens are —– characteristics
inherited
The blood group genes (via mRNA) either (2):
- code for red cell membrane
proteins directly
OR
- code for enzymes which cause the
production of specific red cell
membrane carbohydrate sugars
2 examples of why blood group systems are so important (2)
- sensitising events
- after a blood transfusion when
exposed to antigens you lack - during pregnancy, when fetal RBCs
expressing antigens mother doesnt
have (fathers) cross into maternal
circulation
Blood group (allo) antibodies: sensitising events result in (4):
- immediate catastrophic
intravascular haemolysis via
complement activation (ABO
incompatability) - delayed haemolytic transfusion
reactions - haemolytic disease of the foetus
and newborn (HDFN) - problems in selecting blood for
regularly transfused patients
The ABO System
- ABO antigens are the most
important blood group in relation
to transfusion - also expressed on most endothelial
and epithelial membranes - 4 main groups: A, B, AB, O with
racial variation in population
frequency
The structure of ABO blood antigens
- RBC glycoproteins/lipids have a
terminal sugar fucose - in addition, one of 2 enzymes can
add another sugar, either galactose
or N acetylgalactoasmine to the
antigen making B antingen or A
antigen
What type of gene control over blood groups?
Autosomal Co-dominance for A and B alleles
O is recessive
Autosomal co-dominance of A and B alleles
no antibodies for O because not an antigen
Allo antibodies vs auto antibodies
made in response to something foreign vs in response to a self antigen
Which enzyme makes antigen A, which blood group?
- galactose
- makes A antigen found in blood
groups A and AB
Which enzyme makes antigen B, which blood group?
- N-acetylgalactosamine
- makes B antigen found in groups B
and AB
Which enzyme makes antigen H, which blood group?
- no further sugar added to terminal
sugar fucose so no enzyme - makes antigen H
- found in blood group O
Establishing the blood group based on the Antigen: a.k.a”Forward Grouping”
- use a sample of patients RBC (eg
antigen) and react test against
monoclonal anti- A and anti-B
grouping anti-sera - IgM antibodies causes
haemagglutination of the RBCs - appears as clumping and formation
of an aggregate where antigen and
antibody react
Which group is it?
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1,2,3 = O
4,11,12 = A
5,8 = B
Universal Blood Group Donor
- O-
- no antigens to react with
antibodies in the patient’s blood
Universal Blood Group recipient
- AB
- no antibodies in the patients blood
to react with any blood given
ABO blood group
Why do we develop ABO antibodies?
- in the absence of corresponding
antigens, ABO antibodies form
during the first few months after
birth - probably as a result of exposure to
ABH antigen like substance
(diet, environment)*** - antibodies are naturally occurring,
rather than immune - mainly IgM antibodies
Antibodies to blood group antigens are mainly
- IgM or igG
- IgM antibodies agglutinate blood
cells and cause intravascular
haemolysis because complement
system activated - IgG typically binds to incompatible
RBCs but do not directly agglutinate
them - reactions are delayed
Establishing the blood group (2) methods:
- via antigen in serum
- via antibody in serum
Establishing the blood group based on the antibody in the serum: a.k.a “Reverse Grouping”
- employs methods to detect the
antibodies in serum to confirm the
blood phenotype ie double check
the blood group indirectly
70 year old man called John Smith needs a blood transfusion
He is blood group A
What antibodies does he have?
What blood could he be given?
- he has B antibodies
- he can be given blood group A, and
blood group O
Another 70 year old man called James Smith also needs a blood transfusion
He is blood group B
What antibodies does he have?
What blood could he be given
- he has antibodies for antigen A
- he can be given blood group B and
O
Acute Haemolytic Transfusion Reactions due to ABO incompatibility:
- RBC destruction - intravascular
haemolysis - extreme cases lead to:
- cardiovascular collapse/shock
- renal failure
- DIC (disseminated
intravvascular coagulation) - 1/180,000 red cell units transfused
may be ABOi:
- major morbidity in 30%
- 5-10% death
Other blood group systems:
The Rh blood Group System
- Rh antigens are a component of
RBC transmembrane protein - two genes RhD and RhCE are
responsible for the anitgens - The RhD encodes for the
membrane protein with the D
antigen and RhCE encodes for
membrane proteins with c or C and
e or E antigens
How many gene or haplotype combinations are there in the Rh blood group system?
8 possible gene or haplotype combinations
What antigen is the most clinically important fo rthe Rh system?
- D antigen
- you either have the D antigen or
not - the D antigen is a dominant trait
(not DD and dd not gene?) - predominantly IgG anitbodies
Variation of Rh blood group system
- approx 85% of European
population is Rh+ - approx 15% of the population are
Rh- and can therefore make
antibodies to the D antibodies if
exposed to it via transfusion or
pregnancy - antibodies are predominantly IgG
D antigen is —– and ——.
- antigenic (strong reactions with
antibody) - very immunogenic (good at
stimulating the production of anti D
antibody in D negative people who
are exposed to the D antigen
Sensitisation to Rhesus D antigen
in first pregnancy not rapid agglutination in the baby (antbodies for mum pass to baby and cause lysis of RBC) to cause a problem
HDFN
haemolytic disease of the foetus and newborn
Haemolytic Disease of the Foetus and Newborn:
in the second pregnancy, mum already has some antibodies, so more antibodies produced quickly, more pass to baby, more agglutination and lysis of RBC of baby
How can prevent sensitisation (Rhesus) ?
Booking (10-12 weeks gestation) maternal blood samples for ABO and Rh group and red cell alloantibody screen
Give Routine Antenatal Anti D Prophylaxis (RAADP) for RhD-, non-sensitised women
Administration of anti-D IgG to a Rh- mother can protect against sensitisation of a Rh- mother from a Rh+ foetus, by destroying any foetal Rh+ red blood cells in maternal circulation.
- prevents mum making her own anti
D antibodies, product that has been
manufactured hence doesnt cause
haemolysis or cross the placenta in
the same way
28 and 34 weeks or single larger dose at 28-30 weeks
Further doses of Anti-D immunoglobulin after ‘sensitising’ events to ‘mop up’ D antigen that has come over the placenta from mum to baby
Delivery, miscarriage, CVS, amnio, fall, trauma, APH
If a patient has had a sensitising event, what do we do to stop the risk of developing anti- D antibodies?
- Kleihauer test
- Flow cytometry
Kleihaur Test
- sample of mum
- look for foetal cells
- estimate volume
- red cells are foetal blood cells
- pale cells are maternal blood cells
Flow cytometry
- more sensitive test
- checks how much D antigen
present - confirms volume present and gives
more anti-D if needed
Compatibility testing pre-transfusion
- minimum requirement for all
patients: check ABO - women of childbearing potential:
RhD neg for RhD neg patients, Kell
neg for Kell neg patients - frequently transfused patients:
extended match - in patients who are found to have clinically significant antibodies, capable of causing transfusion reactions, units that are negative and safe are developed
What can we transufe?
we rarely transufe whole blood
rather blood component therapy makes clinical sense as post patients require a specific element of blood (FFP, cyroprecipitate and buffy coats)
plasma derivatives
Donor Selection and minimising infection transmission
- donor eligibility questionnaire: health, lifestyle, travel, meds
- specific precautions to reduced trnasmission of prio-associated diseases including vCJD
- routine screening: Hep B, HIV, Hep C, syphillis, HTLV
special circumstances: malarial antibodies, west nile virus antibodies
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Transufsion process:
- need for transufsion identified
- blood prescribed
- pt cannulated and blood sent for cross match
- 2 samples required at different times
- lab approves suitable unit
- transport to clinical area
- nurse checks
- transfusion begins, with monitoring
