Blood Groups and Transfusion

Question 1

Why is it important to understand blood groups?

Answer 1

• Safe provision of blood (3million units/year in UK)
• Preventing and managing transfusion reactions
• Prevention of haemolytic disease of the new born

Question 2

Where are red cell antigens found?

Answer 2

On surface of red blood cell

Question 3

How many blood group systems are there?

Answer 3

26

Question 4

What are the most important blood group systems?

Answer 4

ABO and Rhesus the most important

As Kell, Duffy, Kidd, MNS etc less likely to cause clinical issues

Question 5

What causes an antibody antigen reaction?

Answer 5

Antibody produced by B cells in response to non-self antigens presented to T cells

Question 6

What two antibodies produced are important in antibody-antigen reactions?

Answer 6

• 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

Question 7

What structure is human IgM made up of?

Answer 7

A pentameric polypeptide chain structure

Question 8

Describe the genetic origin of the ABO system

Answer 8

• 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

Question 9

How do ABO antigens differ?

Answer 9

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

Question 10

What are the naturally occurring antibodies present in those with O type blood?

Answer 10

Anti-A, Anti-B

Question 11

What are the naturally occurring antibodies present in those with A type blood?

Answer 11

Anti-B

Question 12

What are the naturally occurring antibodies present in those with B type blood?

Answer 12

Anti-A

Question 13

What are the naturally occurring antibodies present in those with AB type blood?

Answer 13

None

Question 14

What is the percentage breakdown of the blood type of the population of the UK

Answer 14

O: 46%

A: 42%

B: 9%

AB: 3%

Question 15

How was blood type assessed in the past?

Answer 15

On a glass tile they present differently when exposed to anti-A, anti-B and anti-AB antibodies

Question 16

How is blood type assessed now?

Answer 16

Using a series of small tubes containing different antibodies, blood that interacts with the antibodies will rise, others will sink (?)

Question 17

What antigens are present in the Rhesus system?

Answer 17

c C D e E

Question 18

Describe the Rhesus system

Answer 18

• 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

Question 19

How does the Rhesus system explain haemolytic disease of the newborn?

Answer 19

• 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

Question 20

How do you prevent rhesus D immunisation in pregnant mothers?

Answer 20

• 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

Question 21

What foetal monitoring occurs in pregnant mothers to screen for haemolytic disease of newborn?

Answer 21

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

Question 22

What neonatal management options are there for haemolytic disease of newborn?

Answer 22

• 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

Question 23

How is blood cross matched to a patient?

Answer 23

• 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

Question 24

What transfusion reactions can occur?

Answer 24

• 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)

Question 25

What are common errors in transfusion?

Answer 25

• 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