Blood transfusion Flashcards
where does donated blood come from?
Human source only
Why is donated blood a scarce resource?
1 donor can only give 1 pint/unit maximum every 4 months
9000 units of blood are needed every day in the UK
Only has a shelf life of 5 weeks
When are blood transfusions used?
Massive bleeding
Anaemic
Only when no alternative is available
In terms of blood group what does everyone have on red cell membrane?
Common H stem
What do you have if you’re in blood group O?
Only the common H stem, no A or B antigens
What do you have if you’re in blood group A or B?
Common H stem and A or B antigen
How are the A and B antigens formed?
Adding one or the other sugar residues onto a common glycoprotein and fructose stem on the red cell membranes
What determines the antigens?
Corresponding genes
What does the enzyme that A gene codes for do?
Adds N-acetyl galactosamine onto common glycoprotein and fructose stem
What does the enzyme that B gene codes for do?
Adds galactose
In terms of dominance, what are A and B?
Codominant
In terms of dominance what is O?
Recessive- doesn’t code for anything
In terms of antibodies what will each person have?
Each person will have antibodies against anything that isn’t on the own red cells (they are IgM class)
When are these antibodies formed?
From birth naturally
What does it mean that these antibodies are complete?
They fully activate the complement cascade to cause haemolysis of red cells
What would happen if someone was given blood of an incompatible blood group?
It would be fatal- cytokine storm, lysis, cardiovascular collapse and death
How do they test your blood group in a laboratory?
IgM antibodies interact with corresponding antigens to cause agglutination so if group B blood was mixed with group A cells, agglutination would occur so you know he’s not group A
What is the frequency of blood group A in the UK?
42%
What is the frequency of blood group B in the UK?
8%
What is the frequency of blood group O in the UK?
47%
What is the frequency of blood group AB in the UK?
3%
What does RhD positive mean?
You have the D antigen on the cell membrane
What are the genes for RhD groups?
D- codes for D antigen and is dominant
d- codes for no antigen and is recessive
What genotype do you have if you are RhD negative?
dd
What percentage of people are RhD positive?
85%
What blood group is safe for everyone?
O negative
What blood group can only given to people of that blood group?
AB positive
When does someone that is RhD negative make anti-D antibodies?
After exposure to RhD antigen
What are the implications of anti-D antibody formation?
Future blood transfusions have to be RhD negative otherwise would cause delayed haemolytic transfusion reaction
Haemolytic disease of newborn- foetus is RhD positive, anti-D antibodies cross placenta and cause haemolysis in foetus and can cause hydrops fetalis and death
What is hydrops fetalis?
Accumulation of fluid in foetal tissues or body cavities, most severe form- excessive fluid in peritoneal cavity, pleural cavity and pericardial cavities and soft tissue (oedema)
What is in the bag when blood is taken?
Anticoagulant
Why is whole blood no longer routinely given to patients?
Parts are used because:
More efficient- less is wasted
Some components degenerate quickly if stored as whole blood
Putting blood in fridge isn’t good for coagulation factors and platelets
How do you separate blood into parts?
Centrifugation
What is fresh frozen plasma?
When you freeze the plasma within 6 hours of donation, preserving all coagulation factors
If you take fresh frozen plasma and thaw it overnight in a 4 celsius fridge?
It will separate out into cryoprecipitate at the bottom and some supernatant on top
What is cryoprecipitate a very concentrated form of?
Fibrinogen (factor 1) Factor 8 Von Willebrand Factor Factor 13 Fibronectin
What else you can do with plasma?
Put it in a fractionating column and pull of things like albumin and haemophilia factors and anti-D antibodies
This isn’t done in the UK
What temperature is fresh frozen plasma and cryoprecipitate stored at?
-30 celsius
What is the shelf life of FFP and cryoprecipitate?
2 years
When is FFP used?
Bleeding and abnormal coagulation test results
Reversal of warfarin (which inhibits factor 2, 7, 9 and 10)
When is cryoprecipitate used?
Massive bleeding and fibrinogen is low
What temperature are platelets stored at and what is their shelf life?
Room temperature and 5 days but have to be constantly agitated
Do you need to give platelet that match the blood group?
Yes- Wrong group would be destroyed quickly and could cause RhD sensitisation
When are platelets used?
Most haematology patients with bone marrow failure
Massive bleeding
DIC
Low platelets and patient needs surgery
How do you keep blood safe for patients?
Test for infections and questioning for risk behaviour
How do you prevent harm to donors?
Questioning them to exclude risky ones- e.g. heat problems
What infections must all blood be tested for?
Hep B Hep C HIV HTLV Syphilis CMV
What is the problem with testing for infections and what do you have to do as a result of this?
Window period of infections where tests will not show positive
You have to exclude high risk donors and use voluntary unpaid donors
