blood tranfusion Flashcards
define blood group system
Collection of one or more RBC antigens under the control of a single gene or a cluster of closely linked homologous genes
what factors determine the RBC antigens structure
specific sequence of oligosaccharides (3-10 monosaccharides in a chain)
specific sequence of amino acids
how many blood group systems are there?
43
43 blood group systems contains … antigens
345 red cell
Which blood group systems are most clinically relevant
ABO and Rh
Antibodies against RBC antigens cause haemolysis resulting in: (2)
haemolytic transfusion reactions (HTRs)
haemolytic disease of the foetus and newborn (HDFN)
what are HTRs
where incompatible red cells are transfused i.e. transfused RBC has antigen that corresponds to patients plasma antibodies
what is HDFN
where the foetus has a different RBC antigen to it’s mother where mother produces antibody to that RBC crossing the placenta.
what are the two different types of antibodies?
naturally occurring antibodies
acquired alloantibodies
describe ABO antibodies
.naturally occuring
.Their production is stimulated when the immune system encounters the ‘missing’ ABO blood group in foods or in microorganisms.
.ABO antibodies are mostly IgM antibodies that remain as IgM antibodies
describe IgM antibodies
pentameric
The interaction between the pentameric IgM antibody and RBC antigens in vitro produces direct easily visualised clumping (agglutination) of red cells
what can igM antibodies cause
acute HTRs through activation of the complement system resulting in massive intravascular haemolysis
can igM antibodies cause HDFN?
No-igM can’t cross the placenta
what causes acquired antibodies to form
.vaccination
.exposure from mother to foetus
.incompatiable blood transfusion
what antibodies are associated with being acquired
IgG antibodies
describe the structure of IgG antibodies
Y shaped
true or false: IgG antibodies interaction with RBC antigens can’t be visualised in vitro
true
what causes does IgG antibodies have
delayed HTR
Extravascular haemolytic
HDFN
why can IgG antibodies cause HDFN but IgM cannot
IgG antibodies can cross the placenta in contrast to IgM which cannot.
what does the A gene code for?
an enzyme that adds N-acetyl galactosamine (GalNac) to the common H antigen resulting in the A antigen
what does the B gene code for?
enzyme that adds galactose (Gal) to the common H antigen resulting in the B antigen
why can a transfusion of blood from the wrong ABO group be fatal
the PATIENT has anti A or anti B antibodies which activate complement to hamolyse the red cells
what blood group is given in transfusion if type of patient is unknown and why?
O NEGATIVE- lacks both A or B antigens, therefore there is no risk of acute HTR occurring even if a patient has anti-A or anti-B antibodies.
what is Landsteiner’s law
whichever ABO antigens are lacking on a given person’s RBCs, that person will always have the corresponding antibody. e.g B antigen patient has anti A (as there was no A in blood)
when can platelets not of the same ABO blood group be given to a patient
when they are high-titre negative, (don’t have a high concentration of anti A or Anti B antigens)
A patient requires FFP or cyropercipitate but ABO is unknown. Which type may be given AND WHY
AB-HAS NO ANTIBODIES
Which Rh antigen is most significant
D
RhD, the D allele is recessive: true or false?
False-D allele is dominant
Anti-D antibodies are clinically significant as they can cause:
Delayed HTRs (extravascular haemolysis) - if RhD positive red cells are transfused (resulting in anaemia, high bilirubin, jaundice) HDFN - if a RhD negative mother is carrying a RhD positive fetus as the IgG anti-D antibodies can cross the placenta and haemolyse the RhD positive fetal RBCs.
how can we prevent formation of anti D antibodies
ensuring transfusions to RhD negative patients receive RhD negative red cells and platelets transfusions
How are RhD pregnant women with RhD positive babies treated
Anti D-immunoglobulin which works by destroying any RhD positive fetal RBCs in the maternal (mum’s) circulation before she can make her own anti-D antibodies (known as ‘sensitisation’)
true or false: Red cells for transfusion should be of the same RhD type as the patient i.e. RhD negative RBCs for RhD negative patients.
true
true or false: It is harmful to give a RhD positive patient RhD negative blood
False- no harm, just wasteful
Group O RhD positive RBCs are used as emergency blood when a patient’s needs emergency transfusion: true or false?
false: Group O RhD NEGATIVE RBCs are used as emergency blood when a patient’s needs emergency transfusion
define alloimmunity
Alloimmunity is an immune response to nonself antigens from members of the same species,
true or false:Platelets for transfusion should be of the same RhD type as the patient i.e. RhD negative platelets for RhD negative patient
true
FFP or cryoprecipitate of any D type can transfused regardless of the patients RhD type. Why?
These plasma components do not contain any RBCs.
what is the forward group
ABO antigens on their RBCs
what is the reverse group
ABO antibodies in their plasma
define agglutination
formation of clumps of cells or inert particles by specific antibodies to surface antigenic components
All blood donations undergo two types of testing:
group and screen
infection testing
which tests are mandatory for donor blood
HIV,hep B,hep C, hepE,HLTV and syphillis
what ADDITIONAL tests may be performed on donor blood
malaria, T.Cruzii, CMV (virus)
what is the purpose of antibody screening
detect the presence of any acquired alloantibodies the patient may have developed.
(antibodies produced from exposure to foreign RBC antigen)
name two methods of blood donation
whole body donation
aphaeresis (machine collects and separates blood)
what are the 4 main blood components?
Red cells (‘packed red cells’)
Platelets
Fresh Frozen Plasma (FFP)
Cryoprecipitate
what is fractionation
the pooling of plasma donations to form medicinal products
what can plasma be fractioned into?
Human albumin solution
Immunoglobulins
Clotting factor concentrates
what is FFP
FFP contains all the coagulation factors.
Transfusions of FFP are required for treatment of bleeding or to reduce the risk of bleeding in patients with coagulopathies (multiple blood clotting factor deficiencies)
what causes coagulopathies
.dilution ( massive bleeding)
consumption e.g Diseminated intravascular coagulation
what is in cyroprecipitate?
contains fibrinogen, Factor VIII, von Willebrand factor and Factor XIII.
clinical needs for Human albumin solution include:
To replace plasma volume in patients with plasma volume loss e.g. due to burns or trauma
To replace plasma in plasma exchange e.g in the treatment of autoimmune disorders
To initiate diuresis in patient with low albumin e.g. due to liver or kidney disease
What do prothrombin complex concentrates contain
Factors II, VII, IX and X.
PCCs can be used to reverse the effect of warfarin by replacing these deficient coagulation factors: true or false
True: PCCs can be used to reverse the effect of warfarin by replacing these deficient coagulation factors:
PCC’s can be used to treat:
major bleeding and haemorrhage
