What is ICT?
The Indirect Coombs Test, also called Indirect Antiglobulin Test (IAT) is a laboratory procedure. It is performed to identify the presence or absence of antibodies in blood directed against antigens found on red blood cells. This procedure helps to determine compatibility for blood transfusion, Rh incompatibility between a pregnant woman and her child, and the possibility of hemolytic anemia occurring due to any autoimmune disorder.
Why is ICT done?
- At the time of donating blood, tissue, organ, or bone marrow or while getting registered as a potential donor
- Before receiving a blood transfusion or blood components transfusion to determine compatibility with donated blood
- Before pregnancy and during pregnancy to determine the risk of incompatibility between the mother and fetus
- To determine if hemolytic anemia is caused due to an autoimmune disorder
What does ICT Measure?
The red blood cells have specific antigen markers present on their surface. These marker antigens are glycoproteins and help the body to recognize its own type of red blood cells (RBCs). Antibodies are naturally produced against incompatible RBC antigens when there is exposure to incompatible red blood cells. The three most common antigen markers found on RBCs are A, B, and Rh. The presence or absence of these antigen markers is used to determine the blood group of a person.
Blood transfusion between incompatible blood types causes an antigen-antibody reaction which causes the RBCs to clump together (agglutination) and this results in their destruction. Hence, blood groups of donor and recipient must match to ensure the success of the blood transfusion or organ transplant. Agglutination may also occur due to Rh incompatibility between a Rh-negative pregnant woman (who is having Rh antibodies because of previous sensitization) and her Rh-positive child which may cause antibodies in the mother to cross the placenta and attack the RBCs of the fetus. In some autoimmune disorders, antibodies are produced against antigens on the body’s own RBCs. These antibodies may attack the ‘self’ RBCs and cause agglutination.
The Indirect Coombs Test is performed on the principle of the antigen-antibody reaction between incompatible blood groups. The collected blood specimen is treated with a large range of collected or synthetic human RBC antigens and observed under a microscope. If agglutination (clumping) of RBCs is seen upon treatment with a particular antigen, antibodies against that antigen are already present in the blood specimen. Antibodies against RBC antigens A and B occur naturally, while antibodies against other RBC antigens are produced upon exposure to the corresponding antigen. A similar test called the Direct Coombs Test is performed to detect the presence of antibodies (bound to RBCs) against the body’s own RBCs (autoimmune antibodies) that may be the cause of autoimmune hemolytic anemia.
How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood from a blood vessel in your arm. The healthcare provider will tie an elastic band around your arm to make the blood vessels swell with blood. This makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You will feel a tiny pinprick during the procedure. Blood samples once collected will then be sent to the laboratory.
Is there any risk associated with this test?
There is no risk associated with the test. However, since this test involves a needle prick to withdraw the blood sample, in very rare cases, a patient may experience increased bleeding, hematoma formation (blood collection under the skin), bruising, or infection at the site of the needle prick.