Blood Transfusion Flashcards
(39 cards)
What are the sources of blood donations
Human
1 donor - 1 pint of blood every 4 months
When are blood donations used
When there is no safer alternative
e.g. Massive bleeding - plain fluid not sufficient
Anaemia - iron/B12/folate not appropriate
Describe molecular structure of the ABO blood groups
A and B antigens on red cells are formed by adding 1 or other sugar residue onto a common glycoprotein and fucose stem
Group O has neither A or B sugars (stem only)
Describe the genetics of the ABO blood groups
Antigens determined by corresponding genes
A-gene codes for enzyme which adds N-actyl galactosamine to common glycoprotein and fucose stem
B genes - enzyme adds galactose
A + B = co-dominant
O = recessive
Describe the antibodies against ABO antigens
Antibodies present for antigens not in the body
IgM is natural and activates fully the complement cascade for haemolysis of red cells
How is IgM used for cross matching
IgM antibodies interact with the corresponding antibodies -> agglutination
e.g. B has antibody A, so added to group A there will be clumping = incompatible
What are the proportions of ABO groups in the UK population
A - 42%
B - 8%
O - 47%
AB - 3%
Which antibodies are found in the plasma for the ABO groups
A - anti-B
B - anti-A
O - anti-B, anti-A
AB - none
What are the steps of finding a blood donor that matches the patient
- Patient blood sample (plasma + cells)
- ABO group (test with anti-A and B)
- Select donor unit of the same group
- Cross match - patient’s serum mixed with donor cells
Which RH group is most important and what are the types of this
RhD RhD positive (D antigen) or RhD negative
What are the genes for RhD groups
D - codes for D antigen on RC membrane
d - codes for no antigens and is recessive
What proportion of the UK population are RhD positive
85%
15% negative
Describe the RhD antibodies
Those who lack RhD antigen can make anti-D antibodies after exposure to the antigen (transfusion or pregnancy with RhD positive foetus)
Anti-D antibodies = IgG
What are the implications of anti-D antibodies
Patient must have RhD -ve blood (otherwise anaemia, high bilirubin, jaundice)
Haemolytic disease of the newborn
Describe haemolytic disease of the newborn (HRN)
RhD -ve mother (anti-D), foetus is RhD +ve, mother’s IgG anti-D antibodies cross the placenta and causes severe haemolysis of fatal red cells
Severe - hydros fetalis, death
What is important in the treatment of RhD group patients
Avoid RhD -ve patients from making anti-D
- transfuse blood of the same RHD group
Describe the other red cell groups (other than ABO, RhD)
C,c,E,e
Kell, Duffy, Kidd
8% of its transfused will form Ab to one or more of these antigens
How do we know if the patient needs antigen negative blood
Before each transfusion episode the patient’s blood sample is tested for Ab
Therefore there is an antibody screen of plasma as well as ABO and RhD group testing
Why would a patient need antigen negative blood
Patients who form Ab to other cell group antigens
Corresponding antigen-negative blood needed to reduce risk of delayed haemolytic reaction
How is blood prepared from donation
Collected in a bag with anticoagulant
Red cells become concentrated as the plasma is removed (avoids overloading patients)
Centrifuge the whole bag for red cells to fall to the bottom, platelets middle and plasma top
What are the advantages of not giving whole blood to patients
More efficient - less waste as patients do not need all the components
Some components degenerate quickly is stored as whole blood
What are the 3 forms of plasma from blood donation
Fresh frozen plasma
Cryoprecipitate
Plasma for fractionation (not UK) -> albumin
Describe the red cell component of blood donation
Plasma removed
Shelf life of 5 weeks at 4 degrees
Blood giving set used - filters clumps and debris
Rarely frozen cells needed
Describe the fresh frozen plasma
300ml = unit -30 degrees storage (frozen within 6hrs for coagulant factor preservation) Shelf life 2 years Thaw for 20-30 minutes 12-15ml/kg dose (3 units) Blood group is not required
