Blood group antibodies and antigens

Question 1

What does a Ab-Ag reaction lead to in the body?

Answer 1

Leads to destruction of the cell via 1 of 2 routes:
-Intravascular haemolysis
-Extravascular haemolysis

Question 2

What happens in intravascular haemolysis?

Answer 2

Where the reaction causes direct cell death as the cell breaks up in the blood stream

Question 3

What happens in extravascular haemolysis?

Answer 3

Where the reaction indirectly kills the blood cells, where the liver and spleen remove cells opsonized by Ab

Question 4

What happens to Hb when blood cells are destroyed?

Answer 4

-When the blood cells are destroyed, the Hb inside is released
-Free Hb can bind to haptoglobin, or it may be oxidised and release the haem group, which can then bind to albumin or hemopexin

Question 5

What happens to haem when its released from Hb?

Answer 5

The haem is ultimately converted to bilirubin, and removed in the stool and urine

Question 6

What are the pros and cons of Hb being cleared directly by the kidneys?

Answer 6

Pros
-Fast clearance of Hb
Cons
-Can cause continued loss of hemosiderin and tubular cells it is loaded into

Question 7

What are key features in intravascular haemolysis?

Answer 7

Haemosiderinuria and low haptoglobin levels are key features in intravascular haemolysis

Question 8

What is agglutination?

Answer 8

Agglutination is the clumping together of RBCs to form visible agglutinates

Question 9

What can agglutination identify?

Answer 9

-The presence of a red cell Ag(i.e. blood grouping)
-the presence of an Ab in the plasma(i.e. Ab screening/identification)

Question 10

What can ABO antibodies activate when they react with an antigen and what can this lead to?

Answer 10

ABO Ab can activate complement when they react with an Ag, leading to intravascular haemolysis

Question 11

What are the alleles for different blood group antigens and which ones dominant and recessive?

Answer 11

A, B and O
-A and B are co-dominant
-O is negative

Question 12

If someone has the AA or AO genotype, what antigens do their RBCs have and what antibodies do they produce?

Answer 12

-RBCs will have A antigen
-Produce anti-B antibodies

Question 13

If someone has BB or BO genotype, what antigens do their RBCs have and what antibodies do they produce?

Answer 13

-RBCs will have B antigen
-Produce anti-A antibodies

Question 14

If someone has the OO genotype, what antigens do the RBCs have and what antibodies do they produce?

Answer 14

-RBCs will express No antigens on the surface of their RBCs
-Produce both anti-A and anti-B antibodies

Question 15

If someone has the AB genotype, what antigens do the RBCs have and what antibodies do they produce?

Answer 15

-Express both A and B antigens on their RBCs
-Not produce any antibodies

Question 16

How are RBCs of a patient tested for blood grouping?

Answer 16

-The RBCs are tested with anti-A, anti-B and anti-D Ab in vitro
-Agglutination shows that the Ag complementary to the Ab is present on the RBC
-No agglutination shows the Ag is absent on the RBC

Question 17

How is the plasma of a patient tested in blood grouping?

Answer 17

-The plasma (which will contain the patient’s Ab) is tested with A cells and B cells
-Agglutination shows that a particular Ab is present in the plasma or serum
-No agglutination shows that the Ab is absent

Question 18

What does the RH typing system consist of?

Answer 18

The Rh typing system consists of 50+ Ag, with D being the most important

Question 19

What are people with the D antigen called?

Answer 19

D positive

Question 20

What are people with no D antigen production called?

Answer 20

People who do not produce the D Ag are termed D negative

Question 21

How is D typing tested?

Answer 21

Tested via agglutination

Question 22

How must D type testing be tested?

Answer 22

It must be tested in duplicate (or tested each time a result is needed and compared to the historical result)

Question 23

What is the dominant and recessive allele in RhD?

Answer 23

-D positive is dominant
-D negative is the recessive

Question 24

Why is Rh significant in pregnancy?

Answer 24

Rh Ab are usually IgG and can cause haemolytic disease of the neonate. Anti-D is still the most common cause of severe haemolytic disease of the neonate

Question 25

What does haemolytic disease of the newborn stem from?

Answer 25

Haemolytic disease of the newborn (HDN) stems from a D+ father and a D- mother who’s carrying her first D+ foetus

Question 26

What is the pathophysiology in hemolytic disease of the newborn?

Answer 26

-D Ag from the developing foetus can enter the mother’s blood during parturition
-In response to the foetal D+ Ag, the mother will start producing anti-D Ab
-If the woman then becomes pregnant with another D+ foetus, the anti-D Ab will cross the placenta and damage the foetal RBCs

Question 27

What tests are carried out to identify pregnancies at risk of haemolytic disease of the newborn?

Answer 27

To identify pregnancies at risk of HDN, expectant mothers undergo blood group and Ab screening at their antenatal booking appointment

Question 28

What are the steps involved in the testing for HDN?

Answer 28

-D- women who may need anti-D prophylaxis to prevent HDN are flagged
-Blood group and Ab screening is then repeated at 28 weeks
-Atypical Ab are quantified periodically to assess their potential effect on the foetus

Question 29

What is the treatment for HDN?

Answer 29

-1500 iu of anti-D is given routinely at 28 weeks, with a smaller dose (usually 500 iu) given after a D+ baby
-In some hospitals, 2 smaller (500 iu) doses are given at 28 and 34 weeks instead of the 1 larger dose

Question 30

What are the steps involved in Ab screening?

Answer 30

Patients serum is mixed with 3 selected screening cells, incubated for 15 minutes at 37oc and then centrifuged for 5 minutes