blood transfusion

Question 1

why is the ABO system important?

Answer 1

people have naturally occurring antibodies against any antigen not present on their own RBCs

Question 2

describe the properties of the naturally occurring antibodies that work against any antigen not present on someone’s own RBCs.

Answer 2

IgM class

reactive at 37ºC

capable of fully activating complement (so can cause potentially fatal haemolysis if incompatible blood is transfused)

Question 3

what antibodies are in the plasma of someone with Group A blood cells?

Answer 3

anti-B

Question 4

what antigens are on the red blood cells of someone with Group A blood?

Answer 4

A

Question 5

what antibodies are in the plasma of someone with Group B blood cells?

Answer 5

anti-A

Question 6

what antigens are on the red blood cells of someone with Group B blood?

Answer 6

B

Question 7

what antibodies are in the plasma of someone with Group AB blood cells?

Answer 7

none

Question 8

what antigens are on the red blood cells of someone with Group AB blood?

Answer 8

A and B

Question 9

what antibodies are in the plasma of someone with Group O blood cells?

Answer 9

anti-A and anti-B

Question 10

what antigens are on the red blood cells of someone with Group AB blood?

Answer 10

none

Question 11

what is the relative frequency of the blood groups?

Answer 11

O (most common)
A
B
AB

Question 12

how are A and B antigens on red cells formed?

Answer 12

add one or other sugar residue onto a common glycoprotein and fucose stem (H antigen) on the red cell membrane

group O has neither A nor B sugars; H stem only

Question 13

how are antigens determined?

Answer 13

through corresponding genes

they code for specific enzymes that add specific sugars to the common H antigen

A and B genes are co dominant

O gene is recessive (i.e someone with group A blood could be AA or AO)

Question 14

what does the A gene code for?

Answer 14

enzyme that adds N-acetyl galactosamine to the common H antigen

Question 15

what does the B gene code for?

Answer 15

enzyme that adds galactose to the common H antigen

Question 16

why is group O blood safe to give anyone in an emergency?

Answer 16

no ABO antigens (antibodies cannot attach anywhere and cause agglutination)

Question 17

what is the most important antigen?

Answer 17

D

Question 18

what are the blood groups with reference to the D antigen?

Answer 18

RhD positive (D antigen)

RhD negative (no D antigen)

Question 19

what genes code for the RhD group?

Answer 19

D codes for antigen

d codes for no antigen, recessive

RhD negative means dd genes

RhD positive means either DD or Dd genes

Question 20

what is the relative frequency of the RhD positive and negative blood groups in the UK?

Answer 20

RhD positive 85%

RhD negative 15%

Question 21

what happens if someone with RhD negative blood is exposed to the RhD antigen?

Answer 21

can make anti-D antibodies when sensitised

Question 22

what type of antibodies are anti-D antibodies and why is this important?

Answer 22

IgG class

can cross the placenta

Question 23

how can someone with Rhd negative blood end up being exposed to RhD antigens?

Answer 23

transfusion of RhD positive blood

if an RhD negative woman is pregnant with an RhD positive foetus

Question 24

what are the potential implications of having anti-D antibodies in reference to transfusions?

Answer 24

patient must have RhD negative blood in the future

anti-D would react with RhD positive blood, causing delayed haemolytic transfusion reaction

could cause anaemia, high bilirubin from breakdown of red cells, jaundice etc

Question 25

what are the potential implications of having anti-D antibodies in reference to pregnancies?

Answer 25

if an RhD negative woman with anti-D antibodies is pregnant with an RhD positive foetus, the antibodies can cross the placenta (IgG class)

antibodies attach to the RhD positive red cells in the foetus, cause haemolysis of foetal red cells

severe effects: hydops fetalis, death

less severe effects:
baby survives after birth, high bilirubin levels may cause brain damage or death

Question 26

how can sensitisation of RhD negative patients be avoided?

Answer 26

transfuse blood of same RhD group
(technically no harm to give RhD negative to an RhD positive patient but it is wasteful)

give group O negative blood in an emergency when a patient’s blood group is unknown
(however a very small percentage of blood donated is O negative)