Blood Transfusion Flashcards
How much blood and how frequently can one donor give?
1 unit (1 pint) every 4 months
What glycoprotein and fructose stem is common to everyone?
H stem
What are A and B antigens?
A + B antigens are made by the addition of a sugar residue onto the common H stem
What does the A gene encode?
An ENZYME that adds N-acetyl galactosamine to the H stem
What does the B gene encode?
An ENZYME that adds galactose to the H stem
Describe the inheritance pattern of the ABO blood groups.
A + B genes are co-dominant
O is ‘recessive’ because it doesn’t code for anything at all
Need to be homozygous for O (OO) to be in blood group O
Which antibodies would someone in blood group A possess? Why?
Anti-B antibodies because each person produces antibodies against any antigen that is NOT present on their own red cells.
What class of immunoglobulin are the A/B antibodies?
IgM Naturally occurring (nearly from birth)
What would happen if someone with anti-B antibodies was given B-positive blood?
Anti-A/anti-B antibodies are complete antibodies- thus fully activate the complement cascade to cause haemolysis of red cells
Often FATAL
Can lead to cytokine storm, lysis, cardiovascular collapse + death
In the laboratory, what would you see if you were to mix the plasma of someone of blood group A with the red cells of someone in blood group B?
Agglutination
What are the 2 most common blood groups in the UK?
A (42%)
O (47%)
What is done before transfusion to check that the donor blood and the recipient’s blood is compatible?
Blood sample is taken from the patient + ABO group determined (test with anti-A + anti-B antibodies)
Select a donor unit of the same group
X-MATCH: patient’s serum is mixed with donor red cells – it should NOT react (reaction shows incompatibility)
Which rhesus antigen is the most important?
RhD
Describe the inheritance pattern of the RhD antigen.
Autosomal Dominant
RhD codes for the D antigen
Describe the relative proportions of RhD positive and RhD negative individuals within the population.
RhD positive = 85%
RhD negative = 15%
What can happen when RhD negative people are exposed to RhD positive blood?
They become sensitised + can make anti-D antibodies
What type of antibody are anti-D antibodies?
IgG
What are the implications on future transfusions of an RhD negative individual who has been sensitised to RhD following exposure?
Must be transfused with RhD negative blood or the anti-D antibodies (from 1st exposure) will react with RhD positive blood
This will cause a delayed haemolytic transfusion reaction resulting in anaemia, high BR, jaundice etc.
What is haemolytic disease of the newborn?
If an RhD negative mother generates anti-D antibodies following pregnancy with a RhD positive foetus, then if the next foetus is RhD positive, the mother’s anti-D antibodies (IgG) can cross the placenta + cause haemolysis of foetal red cells.
If severe this can cause hydrops fetalis + death.
About 8% of transfused patients will form antibodies against antigens other than ABO and RhD. What are the implications of this?
Once they have formed antibodies against these other antigens, must use corresponding antigen negative blood, else risk a delayed haemolytic reaction.
What must you always do before transfusion in patients that have developed antibodies other than those against AB or RhD?
Before each transfusion, test patient’s blood sample for red cell antibodies.
So as well as testing the ABO + RhD groups, must do antibody screening of their plasma.
Why is whole blood no longer routinely given to patients?
It’s inefficient- patients don’t need all the components
Some components of the blood will degenerate quickly if stored as whole blood
Why are the red cells concentrated and the plasma removed?
To avoid fluid overloading, which can precipitate heart failure when giving someone red cells
What 3 components is blood 1st separated into via centrifugation?
Plasma
Platelets (+ white cells)
Red Cells
What is fresh frozen plasma (FFP) and what does it contain?
Plasma frozen within 6 hours of donation
All the coagulation factors are preserved
How is cryoprecipitate produced and what does it contain?
Thawing FFP in a 4 degrees centigrade fridge over night produces Cryoprecipitate
Contains:
Fibrinogen + Factor 8
Explain what fractionation is and why it’s useful.
Plasma of many donors is pooled + put into a fractionating column.
Various components e.g. albumin, haemophilia factors + anti-D antibodies can be pulled off.
NOT done in the UK.
How many donors does it take to make one unit of red blood cells?
1
How are red blood cells stored and what is their shelf life? How are they given?
Packed cells with plasma removed
Stored in a 4-degree fridge
Shelf-life = 5 weeks
Given through ‘blood giving set’ which filters clumps
How many donors does it take to make one unit of FFP?
1 (300 ml)
How is FFP stored and what is its shelf life?
Stored at -30 degrees
Shelf-life = 2 years
How is FFP thawed?
Thawed at room temperature for 20-30 mins before use
If thawed at too high a temperature, could cook coagulation proteins
Use within 1/2 an hour of thawing because coagulation factors start to degenerate at room temperature
What is the normal dose of FFP?
12-15 ml/kg = 3 units
Why is it important to know the blood group of the patient before administering the FFP?
To ensure that antibodies in the FFP don’t react with the recipient’s RBC antigens.
If wrong FFP is given it wont kill the patient because the antibodies are quite dilute but it will haemolyse some of the red cells (not ideal)
What are the indications for FFP?
Bleeding + abnormal coagulation test results (PT + APTT)
Reversal of warfarin (e.g. for urgent surgery)– because warfarin inhibits factor 2, 7, 9 + 10
Other conditions/ deficiencies occasionally
How many donors does it take to make one standard dose of cryoprecipitate?
10 donors
What are the indications of cryoprecipitate?
If massive bleeding + fibrinogen is very low
Rarely hypofibrinogenaemia
How many donors does it take to make one standard adult dose of platelets?
4 donors
What machine can be used to get a standard dose of platelets from one donor?
Apheresis– cell separator machine
How are platelets stored and what is its shelf life?
Stored at room temperature (22 degrees)
Must be constantly agitated to prevent them aggregating
Shelf-life = 5 days (risk of bacterial infection)
Why is it important to give platelets of the same blood group to patients?
No need to X-match but need to give platelets of the same ABO blood groups as platelets have low levels of ABO.
Wrong group of platelets would be destroyed quickly.
Giving platelets of the wrong group could also cause RhD sensitization.
What are the indications for giving platelets?
Most haematology patients with bone marrow failure (platelets <10 x 10^9/L)
Massive bleeding
DIC
If very low platelets + patient needs surgery
If cardiac bypass needed + patient is on anti-platelet therapy
1 POOL is usually enough
If a patient is bleeding post-surgery and his platelet count is normal but he has a prolonged PT and APTT, which component(s) does he need?
FFP
If a patient is bleeding post-surgery and his PT and APTT are long and his fibrinogen is low, which component (s) does he need?
FFP (PT + APTT are prolonged)
Cryoprecipitate (Fibrinogen is low)
State some commonly used fractionation products.
Factor 8 + 9 = for haemophilia
Factor 8= for von Willebrand’s disease
Immunoglobulins:
IM: specific e.g. tetanus, anti-D + rabies
IM: normal globulin– broad mix in the population
What can IVIg be used to treat?
Pre-op in patients with ITP (immune thrombocytopenic purpura – IVIg helps prevent the destruction of antibody coated platelets in the spleen + liver) + AIHA (autoimmune haemolytic anaemia)
What is albumin used to treat?
4.5% = useful in burns, plasma exchanges etc.
20% (salt poor) = for certain severe liver + kidney conditions only.
What measures are taken to ensure the safety of donated blood?
Exclude high-risk individuals
Test for infections
Which group of patients are considered universal blood donors?
Group O RhD negative (no antigens on red cells)
Which group of patients are considered universal blood acceptors?
Group AB RhD positive (no A or B antibodies in plasma)
How may anti-D patients be exposed to RhD antigens?
Transfusion of RhD positive blood
Pregnancy with RhD positive foetus
What is the consequence of transfusing RhD negative blood to an RhD positive patient?
No harm
Just wasteful
How are fractionated factor 8 + 9 treated?
Heat treated for viral inactivation
What precautions are taken against transmission of vCJD?
All plasma pooled to make fractionated products obtained from USA
All blood components have white cells filtered out
Which group of patients are considered universal plasma donors?
Group AB (no antibodies in plasma)
