11. Blood transfusion Flashcards
What is the shelf life of blood?
5 weeks
How much blood can you take from a donor?
1 pint (1 unit) max, every 4 months
When is blood used as a treatment?
- When there is no safer alternative
- During a massive bleed
- Anaemic patients - if iron/B12/folate not appropriate
Which red cells are H antigens found on?
All red cells
How are A and B antigens formed?
• Adding sugar residues to a common glycoprotein and fucose stem
Which antigens do group O people have?
Only H stem
Which enzymes do the ABO blood groups code for?
- A gene - N-acetyl galactosamine transferase
- B gene - galactose transferase
- A and B - co-dominant (both genes => both chains)
- O - recessive: may carry O and A/B but A/B will be dominant
Why can an ABO incompatible transfusion be fatal?
- Patient has corresponding antibody e.g. group A has anti-B antibodies, group O has anti-A and B antibodies
- IgM interact
- Activation of complement cascade
- Haemolysis of red cells
How do you cross-match blood groups?
- Mix patient serum with donor red cells
- Agglutination=> incompatible
- Due to antibody interacting the red blood cell antigens
What is the most important RH blood grouping?
• RhD positive (D antigen)
- presence is dominant
• RhD negative (no D antigen)
When are antibodies made against antigens in blood grouping?
• Antibodies against antigens we lack are made from birth in ABO
• Made from first exposure for all other blood grouping systems - including RhD
• RhD negative can only make anti-D antibodies after exposure to RhD antigens
- by transfusion
- during pregnancy
What type of immunoglobulins are anti-D antibodies?
IgG
What type of antibodies does an RhD positive person produce after exposure to RhD negative blood?
None
A RhD negative person is exposed to RhD positive blood, when and how will they react?
• Won’t react first time
• React next time given blood
- new anti-D antibodies interact with second transfusion of RhD positive blood
• Won’t cause death as IgG doesn’t go through the complement cascade
• Slower, extravascular haemolysis
• Still harms the patient - jaundice, free Hb from red cell lysis damages renal tubules => renal failure
When is there a danger to the foetus in relation to the RhD blood group?
- RhD negative mother has transfusion of RhD positive blood
- Mother makes anti-D antibodies
- If foetus is RhD positive, mother’s IgG can cross the placenta => haemolysis of foetal red cells
- If severe: hydrops fetalis (severe oedema) => death
What blood type is used as emergency blood when the patient’s blood type is not known?
O negative
How will a baby with hydrops fetalis be affected if it makes it to birth?
- Anaemia may still be a problem
- Bilirubin needs to be broken down by liver (previously dealt with by mother)
- Liver can’t cope
- Bilirubin crosses BBB and causes brain damage
- Death
How is blood given to a patient?
- 1 unit of blood collected into a bag with anticoagulant
- No longer give whole blood - patient doesn’t need all of it and some components degenerate quickly if whole
- Split into: red cells, plasma (antibodies and coagulation factors), buffy coat (WBCs, platelets)
- Red cells are concentrated and plasma is removed - avoid fluid overload
- Split by centrifuging
At what temperature are red cells stored?
• 4’C
• Rarely frozen
- done for rare groups
- poor recovery on thawing - lose up to half the dose
How is fresh frozen plasma stored and adminstered?
- Frozen to preserve coagulation factors
- Stored at -30’C within 6 hours of donation, shelf life of 2 years
- Thaw approx. 20-30mins before using it
- Give ASAP as coagulation factors degenerate at room temperature
- Dose dependent on patient’s weight: usually 3 units
- Blood group important - may cause a bit of haemolysis
When do we give fresh frozen plasma?
- Patients who are bleeding due to abnormal coagulation factors
- Patient with abnormal coagulation test results
- Reversal of warfarin e.g. for urgent surgery
- Other conditions occasionally
What is cryoprecipitate and when is it used?
- Residue that remains when you thaw FFP slowly (at 4-8’C overnight)
- Precipitate at the bottom
- Contains fibrinogen and factor 8
- Stored the same as FFP
- Standard dose - from 10 donors = 2 packs
- Used in massive bleeding events
- People with very low fibrinogen
- Rare conditions e.g. hypofibrinogenaemia (hereditary)
How are platelets stored?
• 1 pool from 4 donors, or 1 donor by apheresis (cell separator machine)
• Stored at 22’C, shelf life of 5 days (risk of bacterial infection)
• Blood group important
- low levels of ABO antigens on platelets
- RBC contamination can cause RhD sensitisation
When do we give platelets to a patient?
- Mostly haematology patients with bone marrow failure
- Massive bleeding or acute DIC
- Very low platelets + patient needs surgery
- Cardiac bypass surgery + patient is on anti-platelet drugs
- 1 pool usually enough
What fractionated products are used in blood transfusions?
Factor 8 and 9
• haemophilia A and B
• Factor 8 for vW disease
• heat-treated - viral inactivation
Immunoglobulins
• IM - specific: tetanus, anti-D, rabies
• IM - normal globulin, broad mix of antibodies from the pop. (e.g. hep A virus)
• IV - broad mix of antibodies, pre-operative patients with ITP or AIHA
Albumin
• 4.5% - useful in burns (loss of fluid), probably overused though
• 20% - severe liver and kidney conditions - kidney tubules become porous => proteins excreted => poor oncotic pressure
Which infections must be tested for before using blood for donation?
- Hep B
- Hep C
- HIV
- Syphilis
- HTLX
- Hep E
- Some also test for CMV
How reliable are tests for infections in blood for donation?
• Not 100% perfect • Certain infections detectable after a certain amount of time - window period • Cannot rely on testing - therefore exclude high risk donors - use voluntary, unpaid donors
Can prion disease variant CJD be transferred by blood transfusion?
- Yes - can lead to death
- Filtering out the white cells (leucodepletion) can reduce the risk as they are essential for uptake of vCJD into the brain
