Blood Groups and Transfusion Flashcards
Why is it important to understand blood groups?
- Safe provision of blood (3million units/year in UK)
- Preventing and managing transfusion reactions
- Prevention of haemolytic disease of the new born
Where are red cell antigens found?
On surface of red blood cell
How many blood group systems are there?
26
What are the most important blood group systems?
ABO and Rhesus the most important
As Kell, Duffy, Kidd, MNS etc less likely to cause clinical issues
What causes an antibody antigen reaction?
Antibody produced by B cells in response to non-self antigens presented to T cells
What two antibodies produced are important in antibody-antigen reactions?
- IgG antibodies mainly after exposure to blood transfusions or foeto-maternal transmission
- IgM antibodies occur due to components in food which mimic A and B antigens
What structure is human IgM made up of?
A pentameric polypeptide chain structure
Describe the genetic origin of the ABO system
- FUT1 and FUT2 genes (chromosome19) code for H substance
- A and B genes (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
How do ABO antigens differ?
In their sugars:
O antigen has a standard antigen with no added sugars
B antigens are O antigens that have undergone the action of a B type enzyme and have galactose sugar added
A antigens are O antigens that have undergone the action of an A type enzyme and have N-Acetylgalactosamine added
What are the naturally occurring antibodies present in those with O type blood?
Anti-A, Anti-B
What are the naturally occurring antibodies present in those with A type blood?
Anti-B
What are the naturally occurring antibodies present in those with B type blood?
Anti-A
What are the naturally occurring antibodies present in those with AB type blood?
None
What is the percentage breakdown of the blood type of the population of the UK
O: 46%
A: 42%
B: 9%
AB: 3%
How was blood type assessed in the past?
On a glass tile they present differently when exposed to anti-A, anti-B and anti-AB antibodies
How is blood type assessed now?
Using a series of small tubes containing different antibodies, blood that interacts with the antibodies will rise, others will sink (?)
What antigens are present in the Rhesus system?
c C D e E
Describe the Rhesus system
- Antigens c C D e E
- coded for on chromosome 1 and inherited as a triplet eg cDe
- ‘Rhesus negative’ implies D negative - other antibodies are referred to less
- No naturally occurring antibodies but can develop in response to pregnancy or transfusion
How does the Rhesus system explain haemolytic disease of the newborn?
- Foetal red cells carrying antigens from the father transferring to maternal circulation
- Mother produces IgG antibodies to eg D, c, E, Kell
- Antibodies cross the placenta causing anaemia, jaundice, brain damage or foetal death
How do you prevent rhesus D immunisation in pregnant mothers?
- Anti-D prophylaxis given to D negative mothers at 28 weeks and delivery (40 weeks) and after obstetric “events”
- Kleihauer test looks for foetal cells in maternal circulation (acid elution of Hb- fetal Hb is more resistant –shown on blue arrows
- Foetal monitoring by ultrasound
- Can receive intra-uterine transfusion
What foetal monitoring occurs in pregnant mothers to screen for haemolytic disease of newborn?
Foetus of mother with significant red cell antibodies can be monitored for anaemia eg
Flow in middle cerebral artery Ascites
Liver and spleen size
Umbilical cord sampling for blood count/blood group and antibody level
What neonatal management options are there for haemolytic disease of newborn?
- Clinical assessment
- Blood count and reticulocytes/group/red cell antibodies/bilirubin/direct Coombes test looking for membrane-bound antibody
- Allow antibodies to decline
- Phototherapy to increase bilirubin conjugation
- Top-up or exchange transfusion
How is blood cross matched to a patient?
- Donor blood is checked for ABO, rhesus D and often other antigens and the bag is labelled. Also microbiology screening- HIV, Hepatitis etc
- Recipient’s blood is checked for ABO and rhesus D group and the plasma screened for antibodies against a panel of red cell antigens
- Recipient’s plasma is mixed with donor red cells to check for agglutination
What transfusion reactions can occur?
- Acute haemolytic reactions (pre-existing antibodies) usually due to miss-matched blood, ABO most serious
- Delayed haemolytic reactions (new antibodies formed following transfusion)
- Urticaria or anaphylaxis (drugs or plasma proteins)
- Febrile reactions (HLA antibodies)
What are common errors in transfusion?
- Failure to establish patient identity and/or label tube incorrectly when taking blood
- Lab errors eg incorrect sample used or antibodies not working
- Failure to perform bedside check of patient identity when administering blood
