During the development of the baby, there is an interaction between the baby’s blood and the mother’s blood. The direct and indirect Coombs test is a blood test that plays a very important role in the health of babies born to couples with different Rh factors (positive or negative blood type), as it can detect antibodies in the mother’s body, which is vital for the healthy growth of the child in the womb even before conception. But what about you? Do you know what the direct or indirect Coombs test is? And do you know what could affect the life of the fetus growing in this woman’s womb? Let’s talk about that then!
What Is the Purpose of the Direct and Indirect Coombs Test?
We all have different blood types. Type A, B, AB or O and, in addition to these blood types, there are still the positive and negative factors1. In fact, what matters here is not the blood type itself, but the Rh factor (positive or negative) of the parents and the baby. The risk arises during pregnancy when a woman with Rh negative receives a gamete from a partner with Rh positive and then has a baby with a positive Rh factor. The incompatibility of the mother’s Rh negative with the baby’s Rh positive may cause the mother’s body to create antibodies against this different Rh factor, which can lead to expelling the baby or causing problems such as hemolytic disease of the newborn (erythroblastosis fetalis).
Erythroblastosis2 fetalis mainly affects the second child, because the first would not be at risk since there would not be enough antibodies to cross the placenta. However, in a second pregnancy, these antibodies present in the mother’s body cross the placenta and destroy the baby’s red blood cells, leading to serious consequences that can even result in death.
To prevent this problem, the child should receive a negative Rh factor blood transfusion to avoid more serious complications such as severe anemia. This is not uncommon, and that’s why the Coombs test was created. The Coombs test can be direct or indirect. The direct test checks for the presence of antibodies attached to red blood cells. The indirect test checks for antibodies in the serum. It’s used to detect possible incompatibilities in the body against a certain Rh factor by looking for anti-D antibodies present in the mother’s bloodstream.
What Does the Coombs Test Prevent?
A woman with Rh negative blood can have problems with the fetus due to the husband’s Rh factor only if there was a previous pregnancy or miscarriage. Therefore, before getting pregnant again, the woman should undergo treatment for these possible antibodies. The Coombs test is then used to detect antibodies. The reference value for both the direct and indirect Coombs test is NEGATIVE. If any other result is found, the woman must begin treatment during pregnancy, between 28 and 33 weeks of pregnancy. After taking the Coombs test, the pregnant woman receives an injection of anti-D immunoglobulin3.
What Should Be Done If the Test Is Positive?
Women giving birth for the first time or who have found that a miscarried baby had positive Rh factor through the Coombs test receive a shot of anti-D immunoglobulin after birth or after a curettage procedure following a miscarriage. The injection should be given within a maximum of 72 hours, or 3 days after delivery. For women who have recurrent miscarriages, the ideal is to have the direct or indirect Coombs test performed at the doctor’s request to find out if this is the cause of miscarriages. Usually, women with Rh negative are referred for the test by their doctor as soon as the first miscarriage happens.
If the Coombs test is positive, then she must undergo treatment for this condition. Since 2016, Anvisa has banned treatment with the husband vaccine or Cross-Match, a vaccine created from the father’s blood. Although there is much controversy around its use, there are reports that this vaccine helps the woman’s body adapt to the positive Rh factor and prevents future miscarriages or babies being born with developmental problems. Currently, other options are offered, such as the use of cancer medications, for example.
The expected and relieving result for the couple is a negative indirect Coombs test. After facing situations such as the risk of erythroblastosis fetalis and even a miscarriage, many women want to be sure they will provide the best possible conditions so that pregnancy goes smoothly and without complications.
How Is the Test Done?
The Coombs test is performed in a regular laboratory as a routine blood test and the sample is taken from the arm. No preparation or fasting is needed beforehand. Remember, the problem can arise if the first child has a positive Rh factor and the mother is Rh negative.
If the baby’s Rh factor is negative, there will be no issue for the woman in future pregnancies. The anti-D immunoglobulin vaccine is highly effective. It destroys any possibility of antibody development and eliminates the chances of the disease occurring in a subsequent baby.
See also: Prenatal Exams – Why Are They Important?
