Blood groups and Transfusions

Question 1

Red Cell Antigens

Answer 1

• Present on surface of red blood cell

Question 2

Antibody-Antigen reaction

Answer 2

• 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 3

what genes code for the H substance

Answer 3

FUT1 and FUT2 genes (chromosome 19)

Question 4

what do A and B genes on chromosome 9 code for

Answer 4

glucosyl transferases which add further sugar groups

Question 5

o

Answer 5

anti-A, Anti-B 46%

Question 6

a

Answer 6

Anti-B 42%

Question 7

b

Answer 7

Anti-A 9%

Question 8

ab

Answer 8

None 3%

Question 9

Rhesus system

Answer 9

• Antigens c C D e E
• coded for on chromosome 1 and inherited as a triplet eg cDe
• ‘Rhesus negative’ implies D negative
• No naturally occurring antibodies but can develop in response to pregnancy or transfusion

Question 10

Haemolytic disease of the newborn

Answer 10

• 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 11

Prevention of Rhesus D immunisation

Answer 11

• 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

Question 12

Foetal monitoring

Answer 12

• 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 13

Treatment of Rhesus D immunisation

Answer 13

• Foetal monitoring by ultrasound

* Can receive intra-uterine transfusion

Question 14

Neonatal management of rhesus negative children

Answer 14

• 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 15

Cross-matching blood

Answer 15

• 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 16

Transfusion reactions

Answer 16

• 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 17

Errors in transfusion

Answer 17

• 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