The coomb test is a type of blood test that assesses the presence of specific antibodies that attack red blood cells, causing their destruction and possibly leading to the appearance of a type of anemia known as hemolytic.
There are two main types of this exam, which include:
- Direct Coombs test: directly evaluates red blood cells, checking for antibodies attached to the red blood cell and whether these antibodies are derived from the person's own immune system or received by transfusion. This test is usually performed to detect autoimmune hemolytic anemias - See what symptoms may indicate hemolytic anemia; Indirect Coombs test: evaluates the blood plasma, identifying the antibodies present there, and is usually requested in situations of transfusion, to ensure that the blood to be donated is compatible with the recipient.
In addition to anemia, this test can also help identify other diseases that affect blood cells such as leukemia, lupus, mononucleosis and fetal erythroblastosis, also known as hemolytic disease of the newborn, as well as identifying the risk of transfusion reactions. Learn more about fetal erythroblastosis.
How the exam is done
The Coombs test is performed from a blood sample, which must be collected in a clinical analysis laboratory. The collected blood is sent to the laboratory, where direct or indirect Coombs' tests will be performed, depending on the objective.
In the direct Coombs test, the Coombs reagent is added to the patient's blood, allowing the visualization of antibodies that may be linked to the red blood cells. In the indirect Coombs test, the blood is collected and centrifuged, separating the red cells from the plasma, which contains the antibodies. 'Pre-labeled' red cells with antibodies are added to the plasma in order to check whether there are autoantibodies present in the plasma and, consequently, in the patient's blood.
To perform the Coombs test, no preparation is necessary, but some medications can interfere with the result, so it is important to inform the doctor of its use so that guidance can be given on its suspension.
What the result means
The result of the Coombs test is negative when there is no antibody that causes the destruction of the red globes, and therefore it is considered a normal result.
However, when the result is positive, it means that there is an antibody in the blood and, therefore, if the result is positive in the direct Coombs test it means that the person may have a disease such as:
- Autoimmune hemolytic anemia; Mycoplasma infection; Syphilis; Leukemia; Lupus erythematosus; Mononucleosis.
In the case of an indirect Coombs test, the positive result means that the person has an antibody that can cause clots when receiving another type of blood and, therefore, care must be taken when making a blood transfusion. See what the risks of blood transfusion are.
In any case, it is always important that the result is evaluated by the doctor who asked for it, since some background of the person can change the result.
