IAS (Irregular Antibody Screening)

Sometimes, during a transfusion or pregnancy, the immune system can produce antibodies against the red blood cells of the transfused blood or the foetus.

These antibodies are called irregular because they are not normally present, so the test is known as an irregular antibody test, or an antiglobulin test. 

What is Irregular Antibody Screening ?

Our immune system is capable of producing antibodies against foreign agents such as bacteria.  
Sometimes, during a transfusion or pregnancy, it can produce antibodies directed against the red blood cells of the transfused blood or the foetus. These antibodies are called irregular because they are not normally present, so the test is known as an irregular antibody test, or an antiglobulin test.

The frequency and potential severity of the disease varies according to the antibody.

The most dangerous is the anti-D (Rhesus D) antibody.


What is maternal-foetal immunisation ?

The rhesus system is one of the different blood group systems. Although there are many others, this system is the one most often involved in cases of maternal-foetal immunisation. If the mother has red blood cells that are rhesus (RhD) positive (80% of cases), there is no problem. However, if the mother has RhD negative red blood cells (20% of cases), it is useful to know the father’s blood type. If his blood is RhD negative too, there will be no problem in this case either. But if the father is RhD positive, then the foetus may also be RhD positive. 


Normally, there is no contact between the blood of the foetus and that of the mother except in certain cases (delivery, voluntary or involuntary termination of pregnancy, surgery during pregnancy, abdominal trauma). In these situations, the mother’s red blood cells may recognise the foetus’ red blood cells as foreign and produce antibodies that can destroy the red blood cells. There is no risk in the first pregnancy but future pregnancies may be affected. The antibodies produced can cross the placenta and attack the foetus’ red blood cells if they are RhD positive. 

The destruction of red blood cells can be serious for the foetus, so it is very important to monitor irregular antibodies throughout the pregnancy at intervals that will depend on your blood type, medical history and the results of your first irregular antibody screening in early pregnancy.


How is the screening carried out ? 

It is possible to determine the Rhesus D group of the fetus from the mother's blood: fetal cells pass into the mother's blood. Fetal Rhesus D genotyping can be performed by genetic analysis (RHD genotyping) of this fetal DNA. This analysis is done from the 11th or 12th week of amenorrhoea if the father is Rhesus D positive.

The destruction of red blood cells can be serious for the fetus, which is why it is very important to follow up on the RAI throughout the pregnancy. 

Ketterthill pregnancy booklet

Download the full Ketterthill pregnancy booklet and find all the details of your analyses during pregnancy !  


Do you want to be screened ?

Visit one of our medical analysis laboratories.
Ketterthill is a network of nearly 100 laboratories in Luxembourg