Coombs test is a clinical blood test which is done in order to find out if your blood contains certain antibodies which may be harmful to you. These antibodies attach themselves to the red blood corpuscles (RBCs) and can interfere with your immunity system, and also harm you in other ways. In medical terms this test is also referred to as antiglobulin test (AGT).
There are two types of Coombs test - direct and indirect.
The Direct Coombs Test, which is also known as the Direct Antiglobulin Test (DAT) looks for auto-antibodies which have attached themselves on the surface of the red blood cells. These antibodies are sometimes produced in the body due to certain diseases or when you take certain drugs or medicines like procainmide, methyldopa and quinidine. These antibodies are harmful because sometimes they cause anemia by destroying the red blood cells.
This test is sometimes prescribed to diagnose the cause of jaundice or anemia.
The Indirect Coombs Test, which is also known as the Indirect Antiglobulin Test or IAT is used to find out if there are anti-RBC bodies flowing in the blood serum (serum is the clear yellow fluid of the blood, which is left behind after the red blood cells and the clotting materials have been removed from it).
The indirect Coombs test is used during blood transfusion to determine if a blood donor's blood matches with that of the recipient. This is called cross matching and helps to prevent any adverse reaction to a donor's blood. This test is also used to screen pregnant women. Some women have IgG antibodies which can pass through the placenta into the blood of the fetus and prove harmful to the newborn by causing hemolytic disease known as Rh disease.
Blood is taken by means of a syringe, from a vein, usually on the back of the hand or the inside of the elbow. The puncture site should be properly cleaned before, and later covered with a clean gauze or cotton after the blood has been collected.
This blood is then washed in the laboratory so that the red blood corpuscles are separated. These are then tested in successive stages by incubating it with various test serums and the Coombs reagent, which is an antihuman globulin. If there is no agglutination (clumping together of red blood cells), it means the results are positive.
But, if the test is abnormal it means that you have antibodies in the blood that are acting against your red blood cells. This could indicate various ailments such as anemia (either natural or drug-induced), leukemia, syphilis, systemic lupus or a mycoplasmal infection. Your medical practitioner will then proceed with the relevant treatment.