11: Blood Transfusion Flashcards
- List the major blood groups and explain their clinical importance
- Explain the screening of blood donors
- List the blood components used clinically
- Recall the potential side effects of blood and plasma transfusions
?
When do you use blood transfusion?
When plain fluid replacement is not enough
OR
If anaemic - when iron/B12/folate not enough
How do the different blood groups arise?
We all have common glycoprotein and fucose stem on the red cell membrane. This is the H stem (has H antigen on the end)
Blood groups A and B are formed by adding A or B antigens onto the common stem
Group O has NEITHER antigen - just the stem
What does the A gene code for?
Transferase enzyme that adds N-acetyl-galactosamine onto H stem
What does the B gene code for?
Transferase enzyme that adds galactose onto H stem
Feature of the O gene
It is RECESSIVE so you need 1 O gene from each parent or you can’t get group O
What antibodies does the body make against RBC antigens? When does this occur?
Body makes IgM antibodies against whatever antigen you DON’T have.
Occurs near birth
IgM
- pentameric antibodies
- fully activate complement cascade
- causes haemolysis.
IgM works at body temp.
In lab tests, IgM antibodies cause agglutination of RBCs
If you are group A you will have antibodies against group B. Vice versa for group B
If you’re group O, you make both anti-A & anti-B antibodies
What happens if wrong ABO blood group is given?
IgM activates complement cascade
Causes haemolysis
Triggers cytokine storm
Leads to cardiovascular collapse or DEATH
Frequency of blood groups in UK
Group O = 47%
Group A = 42%
Group B = 8%
Group AB = 3%
What antibodies do people with group AB blood have?
None
They dont have anti-A or anti-B antibodies
What is the other blood group type?
RhD positive (if you have D antigen) RhD negative
What are the genes for RhD?
D - codes for D antigen on red cell membrane
d - recessive, doesn’t code for antigen
DD or Dd = RhD positive
dd = RhD negative
Prevalence of RhD groups?
85% RhD positive
15% Rhd negative
What antigens/antibodies do the different RhD groups have?
RhD positive:
- D antigen positive
- NO anti-D antibodies
RhD negative:
- No D antigen
- No anti-D antibodies BUT can make them D if they are exposed to the D antigen. This can occur by:
- Transfusion of RhD positive blood
- Pregnant women with RhD positive fetus
What kind of antibodies are anti-D antibodies
IgG
What happens if you give RhD+ blood to someone who has been exposed previously to RhD+ blood?
Will cause IgG to bind and activate compliment, but doesn’t activate the cascade as far as IgG in ABO groups.
Antibodies will remain bound to RBC - detected by macrophages in spleen - formation of spherocytes
Results in DELAYED haemolytic transfusion reaction
Takes several days to kick in
NOT life threatening
(anaemia, high billirubin, jaundice etc..)
What is haemolytic disease of newborn?
IgG can CROSS PLACENTA
If RhD- mother has anti-D antibodies, and fetus is RhD+ -> causes haemolysis of fetal red cells
If severe: hydrops fetalis or DEATH
What kind of blood is given in emergencies when the patient’s blood group is unknown?
O negative
Group O blood has no antigens so patient will definitely not have any IgM antibodies against it
RhD negative so even if patient has anti-D antibodies it won’t matter
What percentage of donors give Oneg blood?
6-7%
What percentage of patients in hospital will have formed antigens to one or more of the red cell antigens after being transfused?
8%
What tests do you do on a patient before doing a transfusion?
- Check ABO group
- Check RhD group
- ‘Antibody screen’ of their plasma
How do we use the different components of a donor’s blood?
Unnecessary to give WHOLE blood
1 unit of blood -> bag containing anti-coagulant
Centrifuge and separate components
Bottom layer = red cells (given to severe anaemia patients)
Middle layer = platelets (need 4 units worth for it to be sufficient for 1 person)
Top layer = plasma (keep frozen to prevent coagulation factors from disintegrating
We also separate into components to prevent overloading patients with fluid - can cause heart
What can you do with plasma once separated?
FFP - fresh frozen plasma
Cryoprecipitate -> fibrinogen
Plasma for fractionation -> albumin, f8/f9, anti-D
Properties, storage and admin of red cells
Stored at 4 degrees (fridge)
Shelf life 5 weeks (due to possible infection/poorer function of red cells)
Given through blood giving set, which has filters that remove clumps/debris
How are rare blood groups stored?
Frozen BUT when you thaw it, you lose up to a third of the red cells
Properties, storage and admin of FFP
Frozen within 6 hrs of donation to preserve coag factors
Stored at -30 degrees
Shelf life 2 years
Must thaw 20-30 mins before use
Give ASAP after thawing (ideally 1hr) since coag factors degenerate at room temp
Usually give around 3 units of plasma
What happens if you give group B plasma to a group A patient?
Group B plasma will have anti-A antibodies, which will cause a little bit of haemolysis.
This will make them a bit anaemic, but will NOT KILL THEM
When do you give FFP?
- If patient is BLEEDING + abnormal coag test results (PT, APTT)
- > monitor response clinically AND coag tests - To REVERSE WARFARIN for urgent surgery (if PCC is not available)
NOT just to replace fluid loss
What is PCC?
Prothrombin Complex Concentrate
Contains factors 2,7,9,10
Perfect for warfarin reversal as these are the factors that warfarin inhibits
Cryoprecipitate
Frozen plasma -> thawed at 4-8 degrees overnight
Contains fibrinogen + f8
Storage = same as FFP
Standard dose = 2 packs (each pack has 5 donors worth)
When do you give cryoprecipitate?
Massive bleeding + LOW FIBRINOGEN
Platelets
Standard dose = 1 pool from 4 donors
Store at 22 degrees (room temp)
Shelf life = 5 days
Platelets have very low levels of A/B antigens on them, so if you give to wrong blood group platelets will be destroyed by patient’s antibodies.
Platelets must be stored with some of the donor’s plasma. The plasma may have some anti-A/B antibodies.
Could also cause RhD sensitisation
SO give same group when necessary
When do you give platelets?
Mostly bone marrow failure/chemotherapy patients
Massive bleeding
Acute Disseminated Intravascular Coagulation (DIC)
If platelet levels very low and they need surgery
What are the fractionation products? How are they used?
Factor 8 -> Haeomophilia A + von Willebrand’s disease
Factor 9 -> Haemophilia B
Immunoglobulins:
Specific (Tetanus, anti-D, rabies)
Normal globulin (e.g. for Hep A)
Intravenous immunoglobulin (for autoimmune diseases)
Low dose Albumin (burns, plasma exchanges)
High dose Albumin (severe liver/kidney conditions)
What are the criteria for choosing donors?
- Make sure their blood is safe (infections, drugs, disease)
- Make sure its safe for them to donate blood (exclude ppl who have had heart problems)
Testing for infections is NOT failsafe because infections have ‘window period’ where it won’t show as positive.
So exclude high risk donors, use voluntary donors who aren’t being paid
What are the precautions for prion disease (variant CJD)?
CAN be transmitted by transfusion
Precautions:
1. All plasma pools now obtained from USA
2. All components have WBCs removed (in case WBCs are involved in disease)
