The Kleihauer-Betke test is performed when a count of fetal cells present in the maternal circulation is needed. This test is used to predict different types of difficulties that may occur during pregnancy, especially after a mother with Rh-factor blood has had a significant bleeding delivery.
The test is based on the principle that fetal hemoglobin red blood cells are less susceptible to acid elution than adult hemoglobin cells. By applying said acid, it is possible to quantify how much maternal and fetal blood came into contact; this is an important factor when calculating treatment for Rh isoimmunization.
What is the Rh factor?
In order to develop the concept of Rh isoimmunization, it is first important to establish what the Rh factor is. It is also known as D antigen, a protein located on the outer membrane of red blood cells.
Depending on whether it is expressed on this site, people may have Rh + (if they have it) or Rh- (if they do not have it) blood.
In people who do not have it, their immune system will recognize any cell that presents the D antigen (for example, someone's Rh + red blood cell) as a foreign body, and will reject it by generating antibodies that will help to destroy those cells.
It is then that the pregnant mother with Rh- blood enters the scene. If your fetus has Rh + blood, during pregnancy the embryo and the fetus will survive thanks to the constant communication that exists between the circulation of both through the placenta.
By doing this, they are recognized by the maternal immune system, and it generates antibodies against the red blood cells of the fetus. If it is the first pregnancy of this mother, the fetus is not in danger, since the body will be producing the antibodies this time.
However, if that Rh- mother becomes pregnant again with a fetus with Rh + blood, the red blood cells of that fetus will be immediately recognized by the maternal antibodies, and the destruction of each and every fetal red blood cell will begin. In some cases this can be lethal to the fetus before the pregnancy is over.
Kernicterus
In the case of live birth, there is the possibility of irreversible neurological damage due to accumulation of bilirubin in the brain (kernicterus).
In order to treat this terrible complication, there is a vaccine that covers these maternal antibodies, disabling their destructive capacity on fetal red blood cells; this vaccine is known as AntiD or Rhogan, and this is when the Kleihauer-Betke test kicks in.
If this abnormality is detected early, the vaccine is administered in standardized doses during pregnancy.
However, when this pathology is discovered at the time of delivery in a hospital, and during this delivery the mother and fetus suffer significant bleeding, the blood of both comes into greater contact than is normally estimated, and a higher dose of the vaccine is required. to counteract the Rh effect.
To calculate that dose, the amount of blood in both is quantified with the Kleihauer-Berke test, and the dose is titrated based on the test. Massive fetomaternal hemorrhage is usually the cause in up to 1 in 50 stillbirths.
This occurs at the time when there is a break in the placental barrier, allowing blood from the fetal circulation to enter the maternal circulation. Intrauterine fetal death is often one of the reasons why the placental barrier ruptures.
Once the magnitude of the fetomaternal hemorrhage is known, the necessary dose of RhIG is calculated and administered to prevent the mother from producing anti-D antibodies.
What is it for?
Kleihauer-Betke tests can be performed for routine examinations or if disease or toxicity is suspected.
Lab tests can be used to find out if a medical condition is getting better or worse. It is important in predicting pregnancy complications, which could lead to the loss of the baby.
What does it measure?
It is used to analyze maternal blood samples for the presence of fetal red blood cells. The test takes advantage of the fact that baby red blood cells are generally richer in hemoglobin F and hemoglobin F is acid resistant.
This test is used to determine the amount of blood that has been exchanged between the mother and the fetus. Rh- women who are pregnant should have the Kleihauer-Betke test if they have bleeding or risk of bleeding during pregnancy.
How it is performed?
A vein is selected in the arm. The skin of the vein will be cleaned and a needle will be inserted. The blood will be collected in one or more tubes; When enough blood has been collected, the healthcare worker will remove the needle.
The amount of discomfort you feel will depend on many factors, including the person's sensitivity to pain. The patient should tell the person doing the test if they feel they cannot continue with the test.
After a sample is taken, a peripheral blood smear is made from the sample and treated with acid. Maternal hemoglobin dissolves and fetal hemoglobin F remains intact.
After acid treatment, the slides are washed, stained, and microscopically examined. 2000 cells are counted and the percentage of fetal cells is used to predict the percentage of fetal red blood cells in the maternal circulation.
The fetal bleeding volume is calculated to determine the additional amount of RhIG required.
References
- Kleihauer-Betke test, sf, ScienceDirect: sciencedirect.com
- Kleihauer-Betke (KB) Test, sf, MediaLab: labce.com
- Kleihauer-Betke test, (2016), Health Guide: allinahealth.org
- QUICK OBGYN: The Kleihauer – Betke ("KB") test, (2014), Youtube: youtube.com
- Kleihauer-Betke Test, sf, Blood Bank Guy: bbguy.org
- Maternal-Fetal Red Blood Cell Distribution Test, nd, MedlinePlus: medlineplus.gov
- Diann M. Krywko; Sara M. Shunkwiler, (2017), Kleihauer Betke Test, NCBI: ncbi.nlm.nih.gov