Coombs' test is an antiglobulin test used to detect and identify immune antibodies in the blood. We distinguish between the direct Coombs test (BTA) and the indirect Coombs test (PTA). Thanks to it, you can avoid serious post-transfusion complications, diagnose diseases such as brucellosis and listeriosis, and detect a serological conflict between mother and child. What does the Coombs test look like?

Contents:

  1. Coombs Intermediate Test (PTA)
  2. Coombs Test Direct (BTA)

Coombs testis available in two versions - asintermediate Coombs test (POC)or otherwiseindirect antiglobulin test ( PTA)and as be indirect Coombs test (BOC)i.e.direct antiglobulin test (BTA) .

Coombs Intermediate Test (PTA)

Indirect PTA Antiglobulin Test is performed as part of the blood group test. It is used to detect in plasma antibodies against erythrocyte antigens other than A and B. On its basis, it is possible not only to detect the presence of antibodies, but also to identify them and determine which antigens they bind to.

In what cases is the PTA test performed?

  • Before blood transfusion - if the recipient had immune antibodies against the donor cells, they would destroy them. Blood transfusions are not allowed in such a situation.
  • After a transfusion reaction (e.g. if the patient has received the wrong blood by mistake), i.e. if the patient develops symptoms such as: fever, back pain, rash, blood in the urine, jaundice or confusion.
  • For pregnant women to detect a serological conflict between her and her baby. A serological conflict can have serious consequences, so it is important to take appropriate measures in advance, e.g. prepare hospital staff for a blood transfusion. The indirect Coombs test also gives knowledge about other, atypical, antibodies in the mother's blood that, for example, could pass through the placenta into the baby's blood, attack the baby's red blood cells and cause haemolytic disease in the fetus and newborn. PTA is performed in the first trimester of pregnancy, and if the result is negative, it will be done again around week 30. When the mother has no antibodies but is Rh negative, there is a risk of developing it at some point in timeserological conflict, therefore, in this case, the PTA test is repeated three times during pregnancy. On the other hand, when the PTA result is positive - which means that there are antibodies in the mother's blood - the woman has to undergo more tests. However, not all antibodies represent a serological conflict, so if any antibodies are detected, they must be identified. Serological conflict means anti-D antibodies.
  • In patients with autoimmune haemolytic anemia, i.e. when the body produces antibodies against its own erythrocyte antigens. This may occur in the course of diseases such as lupus erythematosus, lymphocytic leukemia, mononucleosis, as well as Mycoplasma pneumoniae infections. It sometimes also happens that haemolytic anemia is caused by the administration of certain drugs, e.g. penicillin.
  • In the diagnosis of brucellosis and listeriosis.

What is the PTA test?

To perform the Coombs test, it is enough to collect venous blood. This can be done at any time of the day without any special preparation. A positive result means the presence of antibodies to red blood cell antigens, while a negative result excludes their presence.

Worth knowing

A serological conflict occurs when the mother is Rh- and the baby is Rh +. If no conflict arises during pregnancy, the child's blood group and blood factor are tested after delivery. If the child is Rh +, the woman must be given anti-D immunoglobulin prophylactically within 72 hours. This will eliminate the blood cells with her baby's D antigen from her bloodstream, helping to prevent a serological conflict in the next pregnancy. A serological conflict occurs when some blood from an Rh + baby has entered her bloodstream. It usually happens during childbirth, both by the forces of nature (less often) and by caesarean section, but also as a result of: amniocentesis, miscarriage, fetal blood collection, hemotherapy, detachment of the placenta, etc.

Coombs Test Direct (BTA)

BTA is used to detect antibodies on blood cells, which coat erythrocytes and attach to their antigens. This test detects the presence of antibodies but tells nothing about their source and type. The rule of thumb is that the more antibodies there are on the red blood cells, the stronger the BTA response.

In what cases is the BTA test performed?

The direct Coombs test can be helpful in determining the cause of autoimmune haemolytic anemia, in the diagnosis of hemolytic disease of the fetus and newborn due to serological conflict, and in explaining the causes of complications after blood transfusion.

What is the BTA test?

The direct antiglobulin test is performed by taking blood from a vein. You don't have to prepare for it in any special way. A positive test result means that the antibodies are attached to the surface of the red blood cells. However, the test does not indicate what type of antibodies they are or what the source of their appearance is.

Important

During a blood transfusion, the recipient's organism always comes into contact with a number of donor antigens. This puts you at risk of developing antibodies to blood cell antigens. The risk increases with each blood transfusion. Patients who have been treated repeatedly with blood transfusions can develop so many antibodies to different antigens that it becomes more and more difficult to select blood for subsequent transfusions.

Category:

Pregnant examinations