Red Blood Cell Isoimmunisation Flashcards
What is red blood cell isoimmunisation?
When a woman that is rhesus-D negative becomes pregnant - child may be rhesus +ve.
If exposed to mum’s blood, The mother’s immune system will produce antibodies to the rhesus-D antigen. The mother has then become sensitised to rhesus-D antigens.
During subsequent pregnancies, the mother’s anti-rhesus-D antibodies can cross the placenta into the fetus. If that fetus is rhesus-D positive, these antibodies attach themselves to the red blood cells of the fetus and causes the immune system of the fetus to attack them, causing the destruction of the red blood cells (haemolysis). The red blood cell destruction caused by antibodies from the mother is called haemolytic disease of the newborn.
How are blood groups classified?
According to its ABO and Rhesus genotype - rhesus consist of three linked pairs, one allele of each pair is dominant to the other:
C/c
D/d
E/e
Individuals inherit one allele of each pair from each parent in a Mendelian fashion
What is the most significant allele in isoimmunisation?
D gene
What does Rhesus D +ve and -ve mean?
only individuals who are DD or Dd express the D antigen are D Rhesus +ve
If an individual has dd they are Rhesus D -ve
What is the effect of rhesus -ve?
immune systems will recognise the D antigens as foreign if they are exposed to it
How does rhesus sensitisation occur?
Small amounts of foetal blood cross the placenta and enter the maternal circulation during uncomplicated pregnancies and particularly at sensitising events, such as delivery
If the foetus is rhesus +ve and the mother is rhesus -ve, the mother will mount an immune response and therefore create anti-D antibodies
What is the effect of sensitisation?
Immunity - permanent.
therefore if the mother’s immune system is again exposed to the antigen e.. subsequent pregnancy, large numbers of antibodies are created
These antibodies can cross the placenta and bind to foetal RBCs, which are then destroyed in the foetal reticuloendothelial system.
This can cause haemolytic anaemia and ultimately death - RHESUS HAEMOLYTIC DISEASE
What other RBC antigens can a similar immune response
anti-c
anti-E
anti-Kell (a non-Rhesus antibody)
How is haemolytic disease of the newborn prevented?
Prevention of sensitisation: intramuscular anti-D injections to rhesus-D negative women.
The anti-D medication works by attaching itself to the rhesus-D antigens on the fetal red blood cells in the mothers circulation, causing them to be destroyed. This prevents the mother’s immune system recognising the antigen and creating it’s own antibodies to the antigen.
Anti-D injections are given routinely on two occasions:
28 weeks gestation
Birth (if the baby’s blood group is found to be rhesus-positive)
Also given if sensitising event: TOP, ectopic, APH, amniocentesis, abdominal trauma
If both parents are known to be D Rhesus -ve, what will the foetus be?
the foetus must also be Rhesus -ve and therefore will be unaffected
How is rhesus type investigated?
Routine NIPT for foetal rhesus type, using maternal blood
Anti-Dis pointless if maternal antiD is already present as sensitisation has already cured
What is done to check for rhesus disease postnatally?
neonate’s blood group is checked - if Rhesus D+ve then anti-D is given to the mother within 72 hours
The Kleihauer test involves adding acid to a sample of the mother’s blood. Fetal haemoglobin is naturally more resistant to acid, so that they are protected against the acidosis that occurs around childbirth. Therefore, fetal haemoglobin persists in response to the added acid, while the mothers haemoglobin is destroyed. The number of cells still containing haemoglobin (the remaining fetal cells) can then be calculated.
What % of women are D rhesus -ve?
15% caucasian women, but fewer African or Asian women
1% of D-Rhesus -ve women have been sensitised in the UK (mostly as a result of omitted or inadequate anti-D
What are the risks of rhesus disease?
as antibody levels rise and cross the placenta - cause haemolysis in the foetus
In mild disease - lead to neonatal jaundice only, or there may be sufficient haemlysis to cause neonatal anaemia
More severe diseases cause in utero anaemia - as this worsens it causes cardiac failure, ascites and oedema = fetal death follows
Rhesus disease usually worsens with successive pregnancies as maternal antibody production increases
What is the management of rhesus isoimmunisation?
Identification of women at risk of foetal haemolysis and anaemia
Assessing if/how severely the foetus is anaemic
Blood transfusion in utero or delivery for affected foetus
