"Coombs test
Why is it done
What is the Coombs Test in Pregnancy for?
At the beginning of pregnancy, pregnant women are subjected to a test to determine the blood group (A, B, AB, 0) and the possible presence of the Rh factor (Rh positive - Rh negative), otherwise known as the D antigen.
In case of incompatibility, the mother can develop an immune response against the red blood cells of the fetus, producing antibodies capable of attacking and destroying the red blood cells of the young organism; the possible and dangerous consequence is anemia, known as haemolytic disease of the fetus (MEN), which in severe cases can lead to intrauterine death.
Hemolytic disease of the newborn (MEN) is characterized by the destruction of fetal red blood cells, due to the transplacental passage of the corresponding IgG-type alloantibodies produced by the mother. In the most severe and characteristic form, hemolytic disease of the newborn is caused by immunoglobulins directed against antigens of the Rh system, but it can also be caused by antibodies directed against other antigens of the red blood cells (antigens of the Kell, Duffy, Kidd, MN Ss, Lutheran).
The consequences of haemolytic disease during fetal life range from the clinical manifestations of "mild anemia to death" in utero. After birth, the main problems are linked to hyperbilirubinemia with strong jaundice and possible neuronal damage.
To check for the presence and concentration of any maternal antibodies against the red blood cells of the fetus, the so-called indirect Coombs test is performed, which should normally give negative results. All pregnant women in the first trimester of pregnancy (by the 16th week) should undergo this screening test, conducted on the mother's blood, especially when the mother's blood type is Rh negative and the father's is Rh positive. In this case, in fact, it is very probable that the blood of the fetus presents the D antigen (therefore Rh positive) and that the maternal organism (Rh negative) consequently develops anti-Rh antibodies.
The problem, in this sense, does not arise if both partners are Rh negative (because the child will also be Rh negative, therefore devoid of D antigen), or if the mother is Rh positive regardless of the father.
Based on these premises, in Rh negative women the Coombs test is repeated every month, while in Rh positive women it is repeated in the third trimester of pregnancy. If antibodies are found during the various checks, their titer should be monitored with fortnightly tests during pregnancy. If you then notice a progressive increase in the antibody titer, a haemolytic disease is most likely developing in the fetus.
When the indirect Coombs test has a positive result, it is necessary to proceed with the identification and titration of the anti erythrocyte antibodies; once identified, the cross-checks on the partner are also very important, in order to evaluate the possible presence of the antigen in the fetus. which the titrated maternal antibody is aimed at.
Hemolytic disease of the fetus due to maternal-fetal incompatibility D (from anti-Rh) is the most severe form and until a few decades ago it represented a major public health problem.
MEN due to AB0 incompatibility between mother and child is quite common, does not occur in the fetus but is an important cause of neonatal jaundice, generally without significant complications
A positive Coombs test is therefore worrying only in some cases, and only if the presence of antibodies exceeds certain levels: the treating doctor will provide more information on this.
Coombs Test, Rh Factor and Hemolytic Disease of the Newborn
Role of the Rh factor in determining MEN
Rh factor is involved in most episodes of haemolytic disease in the newborn. This pathology, linked to the blood group incompatibility between mother and fetus, occurs when the mother is Rh-negative and the fetus Rh-positive.
During pregnancy, small amounts of fetal blood can enter the maternal circulation, but thanks to the placenta it is usually insufficient to evoke an aggressive immune response. The situation is reversed at the moment of delivery, especially if traumatic obstetric maneuvers are performed (for example: the cephalic version of the fetus), or in the event of abortion; in similar circumstances, large quantities of fetal blood come into contact with maternal blood, stimulating a slow process of alloimmunization with the synthesis of alloantibodies (so called because they are destined to fight antigens coming from an individual belonging to the same species).
The risk of Rh antibody haemolytic disease is therefore modest for the first child, but rather high for subsequent pregnancies (provided that the father is again Rh positive). In fact, any re-exposure to the antigen (Rh-positive fetal red blood cells) triggers a secondary immune response with the production of IgG antibodies, capable of crossing the placenta and damaging the red blood cells of the fetus.
PLEASE NOTE: already in the first pregnancy the mother can be immunized against fetal erythrocyte antigens such as the D antigen, for example for previous transfusions of blood or blood products, or for mixed use of infected syringes. For this reason the Coombs test is performed at the beginning of pregnancy on all pregnant women, regardless of blood group.
Positive Coombs test and prophylaxis "
