Blood Transfusions

Question 1

What are the 2 main groups on red cells?

Answer 1

ABO group

Rh (Rhesus) group

Question 2

Which is the most important / major group?

Answer 2

ABO group

Question 3

How does the ABO system work?

Answer 3

All red cells have a common ‘H’ stem (glycoprotein and fructose stem)
Blood group O - only have the common stem, no A or B antigens
Blood group A - common H stem and the A antigen
Blood group B - common H stem and the B antigen
The A and B antigens are formed by adding one or other sugar residues onto the common stem (on the RBC)

Question 4

What are the genes involved in the ABO system?

Answer 4

The antigens are determined by corresponding genes
A gene codes for an enzyme that adds N-acetyl galactosamine onto the common glycoprotein and fructose stem
B gene codes for an enzyme that adds galactose
O gene doesn’t code for anything

Question 5

What are the genes in terms of dominance?

Answer 5

A and B are co-dominant

O is recessive

Question 6

Different blood types and the genes that make them up?

Answer 6

A - AA, AO
B - BB, BO
O - OO
AB - AB

Question 7

Why is the ABO blood group important in terms of antigens and antibodies for blood transfusions?

Answer 7

Each person will have naturally occuring antibodies against any antigen that is not present on their own red cells, e.g. someone with blood group A carries antibodies for the 'B' antigen
Antibodies are present (nearly) from birth, and class IgM

Question 8

What happens if an ABO group antibody meets an ABO group antigen?

Answer 8

They are complete antibodies meaning that they fully activate the complement cascade to cause haemolysis of red cells
Receiving an ABO incompatible transfusion results in the antibody/antigen interaction to be often fatal - i.e. cytokine storm, lysis, cardiovascular collapse and death

Question 9

In the lab, what occurs when the IgM antibodies interact with the corresponding antigens?

Answer 9

Causes agglutination e.g. If the patient is in group B, he will have anti-A antibodies in his plasma. When this plasma is mixed with group A cells, agglutination is seen and this shows that the cells are incompatible

Because the IgM antibodies are so strong, this agglutination can be seen rapidly so you can quickly determine the blood group of the patient

Question 10

Which is the main / most important Rh group tested for?

Answer 10

RhD

Question 11

How does the RhD group work?

Answer 11

Either RhD positive (you have the D antigen) or RhD negative (lack the D antigen)

Question 12

What are the genes involved in the RhD system, and what is their dominance?

Answer 12

D - codes for D antigen (positive) and is dominant

d - does not code for anything (negative) and is recessive

Question 13

The different blood types for the RhD group and the genes that make them up?

Answer 13

Positive = DD or Dd
Negative = dd

Question 14

In times of emergency, which blood group is best to give to a patient with an unknown blood type?

Answer 14

O negative - no antigens, therefore cannot be destroyed by any ABO group / RhD antibodies

Question 15

When are blood transfusions given?

Answer 15

When there is no safer alternative available - must balance benefits and risks
e.g. Massive bleeding - if plain fluids are not sufficient
If anaemic - if iron/folate/B12 are not appropriate

Question 16

How to minimise giving blood transfusions / use blood transfusions efficiently?

Answer 16

If they are deficient in things that are needed to make blood cells then you can just supplement these components rather than going for transfusion
Blood donated separated into different components, e.g. red cells, platelets etc. Target patient’s needs more specifically

Question 17

Which blood type can be used least?

Answer 17

AB positive

Question 18

When do RhD antibodies arise in RhD negative people?

Answer 18

RhD negative can make anti-D antibodies after they have encountered the RhD antigen, e.g. when exposed in a transfusion or in women if they are pregnant with an RhD positive foetus
Anti-D antibodies are IgG antibodies

Question 19

What are some implications to an RhD negative person with anti-D antibodies?

Answer 19

For future blood transfusions - the patient must be given RhD negative blood or else their anti-D antibodies would react with the D antigens causing a delayed haemolytic transfusion reaction (red cells destroyed): leading to anaemia, high bilirubin (released when red cells are broken down), jaundice etc.
HDN (haemolytic disease of the Newborn) - mother’s anti-D antibodies can cross the placenta and cause haemolysis of the RhD positive foetal RBCs. If severe enough, causes hydrops fetalis (build up of fluid in foetal tissue) and death. Or, if the baby survives, after birth they have high bilirubin levels which can cause brain damage

Question 20

What gets damaged especially from the release of Hb during the haemolysis of red cells?

Answer 20

Kidneys - Hb is extremely toxic in the renal tubules in the kidneys hence may cause renal failure

Question 21

What are some examples of other red cell antigens and how are they processed during blood donations?

Answer 21

There are other antigens present on red cells but these antigens don’t tend to be as immunogenicity as the ABO / RhD antigens
E.g. Rh C, c, E, e, some others : Kell, Duffy, Kidd
About 8% of patients transfused will will form antibodies to one or more of these antigens
Once they have formed antibodies against the new antigens, must use corresponding antigen negative blood or else there is a risk of delayed haemolytic reaction (can be severe)

Question 22

When a patient is being given a blood transfusion, how is it known which negative blood they need?

Answer 22

First the ABO and RhD groups are tested

Afterwards, an antibody screen of their plasma is performed to exclude any clinically significant immune antibodies

Question 23

How does the antibody screen work?

Answer 23

Patient plasma is incubated with 2 or 3 different fully typed ‘screening’ red cells, which have all the blood group antigens that matter clinically
If the antibody screen is negative, any donor blood which is ABO and RhD compatible can be given
If the antibody screen is positive, the antibody must be identified with the use of a large panel of red cells
Donor units of blood that lack the corresponding blood group antigen are then chosen for cross matching with the recipient’s plasma prior to transfusion

Question 24

Are ABO and RhD groups the only groups to consider before a blood transfusion?

Answer 24

No

Question 25

Summary of Compatibility Testing before transfusing patients:

Answer 25

​1. Patient blood sample (plasma + cells).
ABO group (test patient’s red cells with known anti-A and anti-B reagents)
RhD group (test patient’s red cells with known anti-D and reagent)
Select donor blood of the same ABO and RhD group
Antibody screen +/- antibody panel, to identify antibody/ies
2​. Cross-match: patient’s serum mixed with chosen donor red cells - should not react: if reacts (agglutinates) = incompatible

Question 26

How are donors chosen? (2 main conditions)

Answer 26

1. To ensure the blood donated is safe for the patient - firstly by asking questions on risk behaviour to exclude them, and secondly by screening for specific infections
2. Aim to prevent harm to the donors - by questioning them to exclude risky donors such as if they have cardiovascular or neurological diseases etc.

Question 27

What is a ‘window’ period for infections?

Answer 27

For infections, where the tests will not show positive results
Therefore you cannot rely on testing and have to: Exclude high risk donors
Use voluntary, unpaid donors

Question 28

What are the tests undertaken on blood donations in the UK?

Answer 28

1. Group & screening: ABO and RhD groups determined. Also, other groups determined e.g. Rh C, c, E, e and the K blood group
   Tested to ensure no strong clinically significant red cell antibodies are present in the donor’s plasma (any transfusions containing plasma will only contain ABO antibodies)
2. Infection testing

Question 29

What are the infection tests performed in the UK on donor blood?

Answer 29

HIV - anti-HIV 1+2 Ab, PCR
Hep B - HBsAg, PCR
Hep C - anti-HCV Ab
Hep E - PCR
HTLV - anti-HTLV Ab
Syphilis - TPHA (Ab test)
(And for some donations: cytomegalovirus - anti-CMV Ab, T.cruzii - anti-T. cruzii Ab, malaria - anti-malaria Ab)

Question 30

What is prion disease and how can it be transmitted?

Answer 30

Involves the the prions of variant Creutzfeldt-Jacob disease (CJD) - found in the membranes of lymphocytes and platelets
4 cases in the UK of vCJD transmitted by transfusion of blood or blood products in humans, where donors who were entirely well, donated, then years later developed vCJD
Currently no blood test to exclude vCJD from donors

Question 31

How can the risk of transmission of prion disease be reduced?

Answer 31

All blood components have white cells filtered out, leucodepleted
This is because white cell membranes can carry vCJD prion and white cells are essential for the uptake of vCJD prion into the brain to cause disease

Question 32

How is blood and how much blood is collected from one donor and what is a unit of blood?

Answer 32

Typically, 450ml of blood collected from one donor, placed into a bag with anti-coagulants
1 unit = whole blood / blood products derived from one single blood donation

Question 33

What components can whole blood be split into, and then what can be split furthermore?

Answer 33

Whole blood - red cells, platelets, plasma

Then, plasma can be split into - FFP (Fresh frozen plasma), cyroprecipitate, albumin (e.g. factor VIII, anti-D etc)

Question 34

Why is whole blood no longer given / stored?

Answer 34

More efficient - less is wasted because patients may not need all the components
Some components degenerate quickly if stored as whole blood
Putting blood in the fridge is not good for the coagulation factors
The fridge is also not good for preserving platelets

Question 35

How are the different components of blood split?

Answer 35

Split one unit of blood by centrifuging whole bag (red cells bottom, platelets middle, plasma top) then squeeze each layer into satellite bags and cut free (closed system)

Question 36

Features of donated red cells:

Answer 36

1 unit comes from 1 donor
They are packed cells with the plasma removed
The red blood cells can be stored in a 4 degree fridge for 5 weeks
The blood giving sets have a filter which removes clumps and debris
You don’t normally tend to freeze blood because it’s inefficient - if you freeze and thaw blood then you lose red cells
But for rare groups/antibodies you will need to freeze the red blood cells (national frozen bank)

Question 37

Why is it better to give red cells rather than whole blood to anaemic patients?

Answer 37

Puts them at risk of fluid overload - especially if they need many units, could push them to heart failure

Question 38

Features of donated platelets:

Answer 38

1 pool from four donors = standard adult dose
It could come from one donor by apheresis (cell separator machine)
It is stored at room temperature (22 degrees celsius) and must be constantly agitated to prevent them from aggregating
As it is at room temperature, the shelf life is only 7 days (because of risk of bacterial infection)
There is no need to cross-match but you do need to give the same blood group because platelets have low levels of ABO so the wrong group platelets would be destroyed very quickly
Giving platelets of the wrong group could also cause RhD sensitisation
Platelets have to be suspended in plasma when they are given because if all the plasma is removed, the platelets would just clump together

Question 39

What conditions may require platelets?

Answer 39

Mostly haemotology patients with bone marrow failure (if platelets < 10 x 109/L)
Massive Bleeding
DIC - there is widespread activation of the coagulation cascade and you get little thrombi forming everywhere and it depletes the amount of platelets you have
If very low platelets and the patient needs surgery
If cardiac bypass is needed and the patient is on anti-platelet drugs
One pool is usually enough - rarely need more

Question 40

Features of donated fresh frozen plasma (FFP):

Answer 40

Freezing the plasma within 6 hours of donation preserves all the coagulation factors (this is FFP)
1 unit from 1 donor (300 ml)
There are smaller packs for children
It is stored at -30 degrees celsius
It has a shelf life of 2 years
It needs to be thawed at room temperature for 20-30 mins before use
If it is thawed at too high a temperature, the proteins could get denatured
Ideally you want to use it within an hour because the coagulation factors will start to degenerate at room temperature
Dose = 12-15 ml/kg = usually 3 units
You need to know the blood group of the patient before administering the FFP to make sure that the antibodies in the FFP don’t react with the red blood cell antigens
There are some ABO antibodies in the FFP
If you give the wrong FFP it is not going to kill them because the antibodies are quite dilute but it will haemolyse some of their red cells which is not ideal

Question 41

What conditions may require FFP transfusions?

Answer 41

It is not only used to replace volume / fluid loss
Bleeding and abnormal coagulation test results (PT, APTT) - monitor the response clinically and with coagulation tests
Reversal of warfarin - e.g. for urgent surgery (this is because warfarin inhibits factor 2, 7, 9 and 10)

Question 42

For FFP what blood group should you give in an emergency?

Answer 42

AB - does not have any of the antibodies

Question 43

Features of donated cyroprecipitate:

Answer 43

FFP thawed overnight in a 4 degrees celsius fridge separates out to cyroprecipitate at the bottom and some supernatant on top
Cryoprecipitate is a very concentrated form of: fibrinogen (factor 1), factor 8, von willebrand factor, factor 13, fibronectin
Storage is the same as FFP: stored at -30 degrees for 3 years
Standard dose = from 10 donors
Indications: if massive bleeding and fibrinogen is very low, or rarely - hypofibrinogenaemia

Question 44

What is plasma fractionation (does NOT occur in the UK) and what are the products of plasma fractionation used for?

Answer 44

Large pool of plasma from 1000s of donors is brought together and fractionated into:
Factor 8 and Factor 9
For haemophilia A and B respectively
Factor 8 for von Willebrand’s disease
They are all heat treated to kill any viruses
Recombinant factor 8 and 9 alternatively are increasingly used, but expensive

Immunoglobulins 
IM (intramuscular): specific - tetanus; anti-D; rabies 
IM (intramuscular): normal globulin - broad mix in population (e.g. HAV)  
IV Ig (intravenous Immunoglobulin): pre-op in patients with ITP (idiopathic thrombocytopenic purpura) and AIHA (autoimmune haemolytic anaemia)  

Albumin
4.5% - useful in burns, plasma exchanges etc.
20% (salt poor) - for certain severe liver and kidney conditions only (this is when they lose masses of proteins)

Question 45

During delivery; the baby’s blood accidentally enters the mother’s bloodstream.
How to prevent the mother’s immune system forming anti-D antibodies against the baby’s RhD positive blood in her bloodstream?

Answer 45

Give the mother an injection of anti-D antibodies
Prevents setting off the mother’s immune response against the baby’s RhD positive blood, and the anti-D antibodies in the injections coat the baby’s blood and the cells are destroyed.