Coombs test: the important antibody test in pregnancy
The Coombs test consists of a blood test used to detect the presence of antibodies capable of attacking red blood cells, therefore important - for pregnant women - to be able to verify the compatibility of the blood group of mother and fetus or, in general, to evaluate the compatibility of blood groups in view of a transfusion or to diagnose forms of anemia.
The Coombs test was devised in 1945 by Cambridge immunologists Robin Coombs (hence its name), Arthur Mourant and Rob Race. When a woman is at the beginning of her pregnancy, she will have to carry out this test in order to determine the possible presence of the Rh factor (which can be positive or negative), also called D antigen.
The D antigen, as well as the AB0 antigen, are found on the surface of red blood cells and are recognized by the body's defense system. If the pregnant woman has a Rh negative blood type and the fetus has a Rh positive blood type, the blood of the mother and the baby will not be compatible. At the first contact between the blood of one and that of the other (whether it happens at the time of childbirth or an abortion or during an "amniocentesis), the woman's body will recognize the fetus as foreign and, at the next pregnancy, it will push the his immune system to produce anti-Rh antibodies in order to destroy the red blood cells of the fetus, perceived as "foreign" and "enemies". This reaction will cause "haemolytic anemia in the fetus."
We therefore understand how important it is to carry out the Coombs test for a pregnant woman: this test will allow to detect the presence of anti-Rh antibodies, diagnosing a possible risk of haemolytic anemia for the child who is about to be born. In this way it will be possible to try to prevent haemolytic disease.
The Coombs test, which can be direct or indirect, is not only used in pregnancy, but also in the case of autoimmune diseases, cancers or to check the compatibility between two types of blood following a transfusion. Let's find out everything there is to know about this test, when to do it and how to interpret the positive or negative results. First, however, here is a video on how to cuddle your little one inside the belly:
When to perform the direct Coombs test?
The Coombs test consists of a simple blood sample, which can be prescribed by the family doctor or a hematologist. It can be of its types: direct or indirect. The direct Coombs test is designed to detect antibodies on the surface of red blood cells and is prescribed to patients suffering from anemia whose origin is not known.
Once the blood has been taken, the red blood cells are isolated and incubated with the so-called "Coombs serum", that is a serum based on human anti-immunoglobulins (Ig), able to recognize the antibodies present on the red blood cell membrane (the famous anti-Rh) If the anti-immunoglobulins bind to the anti-Rh, the test will be positive, if the antibodies are not present and the bond is not obtained the test will be negative.
The direct Coombs test is prescribed for diseases such as infectious mononucleosis, tuberculosis, haemolytic disease of the newborn, rheumatoid arthritis. It is also prescribed to those who have had a supposed transfusion anemia, due to incompatible blood, or an anemia. drug-related haemolytics (usually common after taking some antibiotics).
When to perform the indirect Coombs test?
The indirect Coombs test is used to detect the presence of anti-Rh antibodies in the blood, which can attack and destroy red blood cells. This test is prescribed to those who have come into contact with blood other than their own, therefore - for example - in the case of a transfusion or during pregnancy.
A pregnant woman undergoes this test because the anti-Rh antibodies in her blood, if present, could cross the placenta and attack the red blood cells of the fetus, causing "haemolytic anemia, also called MENF. MENF risks leading to death. intrauterine of the fetus. It is a disease that rarely occurs in the first pregnancy, but it is always good to do this test in the routine control examination within the first trimester, and then repeat it at the 28th week of pregnancy.
How to interpret a positive result?
If the direct Coombs test is positive, it means that the test has detected the presence of antibodies bound to red blood cells. If the test result, on the other hand, is negative, it means that there are no antibodies on the surface of the red blood cells and, consequently, the symptoms that were found have other reasons.
If the indirect Coombs test is positive it means that there are anti-Rh antibodies in the blood. At this point it will be essential for the pregnant woman to have a thorough medical examination that can determine whether the positive result is due to a reaction to a transfusion, to "autoimmunity, to an" infection, to the use of drugs or, indeed, to the " incompatibility between one's blood group and the fetus, which could lead to the development of "haemolytic anemia."
For more information on the Coombs test, you can consult the website of the Istituto Superiore di Sanità.
