Haem 11 - Blood transfusion Flashcards
When do we use blood
Balance between benefits and risks - i.e. when no safer alternative available e.g. if massive bleeding and “plain fluids” not work, if anaemic and B12/Iron/folate insufficient
Describe the basis of the ABO blood groups
All blood has a common H antigen stem.
If A group: A antigen attached onto common H stem
If B group: B antigen attached onto common H stem
If AB: Some stems with A on, some stems with B on
If O group: nothing else added on, just plain H stem
Describe the genes for ABO blood group
A gene - codes for enzyme which adds n-acetyl galactosamine to common H stem (common H stem = glycoprotein and glucose stem)
B gene - codes for enzyme which adds galactose to common H stem
A and B are codominant, O gene is recessive
Everyone has antibodies against any antigen NOT present on own RBC. e.g. I am group B, so I have anti-A antibodies. Which immunoglobulin can cause damage
IgM.
I have IGM-antiA so if I am given group A blood - this would trigger the complement cascade and cause haemolytic of my RBC - can be fatal
NB - in labs IgM antibodies react with their corresponding antigen (e.g. IgM anti-A will react with group A antigens and cause agglutinatination)
Group O = universal donor. What is the universal recipient?
Group AB
What is crossmatching
Add patients plasma against RBC we are going to transfuse - check to ensure no agglutination
Describe RH groups (specifically RhD)
There is RhD positive and RhD negative.
Genes for RhD groups:
- D = codes for D antigen on RBC membrane
- d = codes for no antigen, is recessive
So patient must be homozygous (dd) to be RhD negative.
DD/Dd = RhD positive
85% people positive
Anti-D antibodies are what type of antibodies?
IgG
ABO, pretty much form antibodies straight after birth. With RhD, you can still make anti-D antibody if you are sensitised. How is one sensitised
- Transfusion
- If they’re pregnant with an RhD positive foetus
RhD positive - D antigen present, no anti-D antibody
RhD negative - no D antigen present, can make anti-D if sensitised
Which is the only type of antibody that can cross the placenta?
IgG
What are the implications for a patient if they have anti-D antibodies?
- All future transfusions must be done with RhD negative blood - or else the anti-D would react with RhD positive blood causing delayed haemolytic transfusion reaction - anaemia, high bilirubin, jaundice, etc)
- Haemolytic disease of the newborn (HDN). If mother (RhD neg) has anti-D antibodies - but foetus has RhD positive blood - mothers IgG anti-D can cross placenta —> cause haemolytic of foetal red cells - can be fatal if severe
Transfuse blood of same RhD group.
Y
no harm giving RhD negative to a RhD positive patient - just wasteful
In case of immediate emergency - which blood group is given
O negative
There are other red cell antigen groups. How many?
About 12 - but not all cause clinically significant effects (e.g. haemolysis)
About 8% patients transfused develop antibodies to some antigens - in FUTURE you must use corresponding antigen negative blood - otherwise you risk delayed haemolytic reaction
Before each transfusion episode, what are the checks done
- Test ABO and RhD group
2. Do an “antibody screen” of their plasma
1 unit of blood is collected into bad with anticoagulant. We don’t routinely give whole blood to patients - we use the parts needed. Explain
- More efficient - less waste - patients don’t need all the “components”
- Some components quickly degenerate if stored as “whole blood”
- RBC concentrated as plasma removed -also avoids fluid overloading patients
Blood split up by centrifugation - RBC bottom, platelets middle, plasma top.
What are the different forms of plasma
- Fresh frozen plasma
- Cryoprecipitate (Fibrinogen / F1/8)
- Plasma for fractionation (e.g. albumin, F8/9, Igs, anti-D, etc)
How long is an RBC donation kept for
5 weeks - stored at 4 degrees
Donations given via blood giving set - filters to remove clumps/debris
Describe preservation and storage of fresh frozen plasma (FFP)
- Stored at -30
- 2 years shelf life
- Dose = 12-15ml/kg
- Must thaw approx 20-30 mins before use (too hot = proteins cook)
MUST MATCH - but not deadly, just anaemia + pain if you don’t match as some antibodies still present
Which coagulation factors does warfarin inhibit
2, 7, 9, 10 (stops them being carboxylated)
What are the indications for giving FFP
- Bleeding + abnormal coag test results (PT, APPT) - monitor response, clinically and by coagulation tests
- Reversal of warfarin (e.g. for urgent surgery - though not first line but given in emergency)
- Other conditions
Describe cryoprecipitate
- Contains fibrinogen and f8 (and f1)
- Stored same as FFP = -30 for 2 yrs
Indications for use:
- If massive bleeding and low fibrinogen
- Rarely hypofibrinogenaemia
Describe the use of platelets
- Stored at 22 degrees - room temp and constantly agitated
- Shelf life only 5 days
- NEED TO KNOW blood group - no cross match just choose same group. Can cause RhD sensitisation (as some red cell contamination)
What are the indications to give platelets
- Mostly haematology patients with bone marrow failure (<10 x 10^9/l)
- Massive bleeding or acute DIC
- If very low platelets and patient needs surgery
- If for cardiac bypass and patient on anti-platelet drugs
- 1 pool usually enough
(6. Generally - platelets and FFP overused - limited resource and cost)
