Blood Groups and Blood Transfusion Flashcards
What are red cell antigens ?
Antigens present of the surface of red blood cells. (found in the lipid layer, extracellular)
26 blood group systems
- ABO and Rhesus systems are most important
- Kell, Duffy etc. less likely to cause clinical conditions
Describe an antibody-antigen reaction
Antibody produced by B cells in response to non-self antigens presented to T cells by antigen presenting cells - monocytes, macrophages
IgG antibodies mainly after exposure to blood transfusions or foeto-maternal transmission.
Naturally occurring IgM antibodies present at/soon after birth against antigens that the individual lacks.
Describe the structure of an antibody
Fab region - antigen binding region
Fc region - fraction crystallisable region
State the typical structure of an IgM antibody
Pentamer
Feature of IgM antibodies
IgM antibodies are more dangerous than IgG antibodies in immune hemolysis.
Describe the action of IgM
IgM antibodies can agglutinate red cells
IgM activates compliment and the membrane attack complex rapidly destroys cells
Describe the action of IgG
IgG does not damage circulating red cells.
Fc receptors on splenic macrophages bind IgG-coated red cells, which may then be gradually destroyed.
Describe the ABO system
FUT1 and FUT2 genes (on chromosome 19) code for H substance
A and B genes (on chromosome 9) code for glucosyl transferases which add further sugar groups.
Naturally occurring anti-A and/or B IgM antibodies in individuals lacking these antigens
H substance
Sugar chain that projects out from the cell surface.
Virtually everyone has H substance
(chromosome 19)
Function of A / B genes
Transfer one more sugar group onto the pre-existing chain of sugars (H substance)
(chromosome 9)
Group O
Neither A or B antigens
They have naturally occurring anti-A and anti-B antibodies.
Describe the A / B antigens location
Transmembrane antigens
Stick out into the plasma
Group O
(What antibodies are present ?)
Anti-A
Anti-B
(in plasma)
46% UK
Group A
(What antibodies are present ?)
Anti-B
(in plasma)
42% UK
Group B
(What antibodies are present ?)
Anti-A
(in plasma)
9% UK
Group AB
(What antibodies are present ?)
No naturally occurring antibodies
3% UK
Describe ABO grouping on a glass tile
Positive reaction = clumping of cells
Blood products examples
Plasma reduced cells
Pooled platelet concentrate
Fresh frozen plasma / cryoprecipitate
How is blood grouping carried out ?
Using gel columns
ABO and Rh grouping in micro-titre gel tubes
Positive reaction = cells held high in gel after centrifugation
If a person is blood group O, what ABO antibodies would his plasma contain ?
Anti-A and Anti-B
A person who is group A will have what characteristics on their red cells and in their plasma ?
A antigens on cells
Anti-B in plasma
Describe the Rhesus system
Antigens c C D e E
Coded for on chromosome 1 and inherited as a triplet : e.g. cDe
‘Rhesus negative’ implies D negative
No naturally occurring antibodies but can develop in response to pregnancy or transfusion.
Rhesus negative
D negative
Difference between ABO and Rhesus system
Rhesus system does not have a naturally occurring antibody against antigens we lack.
We only develop them in response to blood transfusion or pregnancy.
What is haemolytic disease of the newborn ?
Foetal red cells carry antigens from the mother and the father (includes Rh antigens).
The baby carries an antigen (from the father) that the mother does not have.
Foetal red cells carrying antigens from the father, transferring to maternal circulation.
Mother recognises these as not her cells, and so can produce antibodies against these.
Describe what happens in haemolytic disease of the newborn
Mother produces IgG antibodies in response to (e.g. D, c, E, Kell)
Antibodies cross the placenta causing anaemia, jaundice, brain damage or foetal death.
Explain how haemolytic disease of the newborn can affect the second pregnancy
In the 1st pregnancy, the Rh- woman has conceived a Rh+ foetus
During labour, foetal red cells leak into the mother.
The foetal red cells survive long enough to elicit an IgG response.
The maternal anti-D antibodies cross the placenta in the 2nd pregnancy and attack foetal red cells.
Describe prevention of Rh D reaction
Via immunisation
Anti-D prophylaxis offered to D negative mothers @ 28 weeks + delivery + after obstetric events.
Function of Kleihauer test
Looks for foetal cells in maternal circulation.
Acid elution (washing out) of Hb - foetal Hb is more resistant - looks darker circles (as Hb is not washed out)
Describe foetal monitoring
Foetus of mother with significant red cell antibodies can be monitored for anaemia :
- flow in middle cerebral artery
- ascites
- liver and spleen size (getting larger)
Umbilical cord sampling for blood count /blood group and antibody level
Treatment of Rh D immunisation
Foetal monitoring by ultrasound
Can receive intra-uterine transfusion
Describe neonatal management
Clinical assessment
- Blood count
- Phototherapy to increase bilirubin conjugation
- Top-up or exchange transfusion
Coombes test
Looks for membrane-bound antibody
- Allow antibodies to decline
- Top-up or exchange transfusion
Describe cross-matching blood
Donor blood is checked for ABO, Rh D and other antigens
Microbiology screening - HIV, Hep B
Recipients blood is checked for ABO and Rh D group. Plasma is screened for antibodies against a panel of red cell antigens.
The recipients plasma is mixed with donor red cells to check for agglutination.
Why is the recipients plasma mixed with donor red cells ?
To check for agglutination
- If there is a reaction the cells will stay at the top of the tube
Typical uses plasma reduced cells
Haematological conditions causing under production of blood :
- Trauma
- GI bleeding
- Childbirth
- Peri-operative
Typical uses for platelets
Marrow failure
Massive haemorrhage
Typical uses for fresh frozen plasma
Liver failure
Massive haemorrhage
Blood transfusion consent
Formal signed consent is NOT taken in the UK
Leaflet and discussion about:
- Risks and benefits
- Alternative options
… but emergency use is valid, even if patient cannot give consent
Describe transfusion reactions
Acute haemolytic reactions (pre-existing antibodies) usually due to miss-matched blood
Delayed haemolytic reactions (new antibodies formed following transfusion)
Urticaria or anaphylaxis
(drugs or plasma proteins)
Febrile reactions
(HLA antibodies)
Which transfusion reaction is most serious ?
ABO mismatch is MOST serious
- Group A individual has less anti-B than a group O individual
Management of acute transfusion reaction
Stop the transfusion
Assess the patient
Return the blood bag, FBC, biochem, blood cultures, 3x transfusion tubes to lab
IV fluids
Monitor urine output, renal function and coagulation
Acute transfusion reaction timings
Most severe reactions are within minutes of starting
What to do in the case of a urticarial reaction ?
Temporarily stop blood
Gove IV piriton
Review 30 minutes
Continue transfusion if settling
Some symptoms of anaphylaxis
Runny nose
Respiratory symptoms
Hives, Itchiness
Heart symptoms
Swelling of tongue, lips etc.
Human errors in transfusion
Failure to establish patient identity and/or label tube incorrectly when taking blood
Failure to perform bedside check of patient identity when administering blood
Lab errors - e.g. incorrect sample used or antibodies not working
