Blood group antibodies and antigens Flashcards
What does a Ab-Ag reaction lead to in the body?
Leads to destruction of the cell via 1 of 2 routes:
-Intravascular haemolysis
-Extravascular haemolysis
What happens in intravascular haemolysis?
Where the reaction causes direct cell death as the cell breaks up in the blood stream
What happens in extravascular haemolysis?
Where the reaction indirectly kills the blood cells, where the liver and spleen remove cells opsonized by Ab
What happens to Hb when blood cells are destroyed?
-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
What happens to haem when its released from Hb?
The haem is ultimately converted to bilirubin, and removed in the stool and urine
What are the pros and cons of Hb being cleared directly by the kidneys?
Pros
-Fast clearance of Hb
Cons
-Can cause continued loss of hemosiderin and tubular cells it is loaded into
What are key features in intravascular haemolysis?
Haemosiderinuria and low haptoglobin levels are key features in intravascular haemolysis
What is agglutination?
Agglutination is the clumping together of RBCs to form visible agglutinates
What can agglutination identify?
-The presence of a red cell Ag(i.e. blood grouping)
-the presence of an Ab in the plasma(i.e. Ab screening/identification)
What can ABO antibodies activate when they react with an antigen and what can this lead to?
ABO Ab can activate complement when they react with an Ag, leading to intravascular haemolysis
What are the alleles for different blood group antigens and which ones dominant and recessive?
A, B and O
-A and B are co-dominant
-O is negative
If someone has the AA or AO genotype, what antigens do their RBCs have and what antibodies do they produce?
-RBCs will have A antigen
-Produce anti-B antibodies
If someone has BB or BO genotype, what antigens do their RBCs have and what antibodies do they produce?
-RBCs will have B antigen
-Produce anti-A antibodies
If someone has the OO genotype, what antigens do the RBCs have and what antibodies do they produce?
-RBCs will express No antigens on the surface of their RBCs
-Produce both anti-A and anti-B antibodies
If someone has the AB genotype, what antigens do the RBCs have and what antibodies do they produce?
-Express both A and B antigens on their RBCs
-Not produce any antibodies
How are RBCs of a patient tested for blood grouping?
-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
How is the plasma of a patient tested in blood grouping?
-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
What does the RH typing system consist of?
The Rh typing system consists of 50+ Ag, with D being the most important
What are people with the D antigen called?
D positive
What are people with no D antigen production called?
People who do not produce the D Ag are termed D negative
How is D typing tested?
Tested via agglutination
How must D type testing be tested?
It must be tested in duplicate (or tested each time a result is needed and compared to the historical result)
What is the dominant and recessive allele in RhD?
-D positive is dominant
-D negative is the recessive
Why is Rh significant in pregnancy?
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
What does haemolytic disease of the newborn stem from?
Haemolytic disease of the newborn (HDN) stems from a D+ father and a D- mother who’s carrying her first D+ foetus
What is the pathophysiology in hemolytic disease of the newborn?
-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
What tests are carried out to identify pregnancies at risk of haemolytic disease of the newborn?
To identify pregnancies at risk of HDN, expectant mothers undergo blood group and Ab screening at their antenatal booking appointment
What are the steps involved in the testing for HDN?
-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
What is the treatment for HDN?
-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
What are the steps involved in Ab screening?
Patients serum is mixed with 3 selected screening cells, incubated for 15 minutes at 37oc and then centrifuged for 5 minutes
