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Coombs Test - Indirect

400
4.8
NABL, CAP
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Overview
Interpreting Results
FAQ's
Coombs Test - Indirect

Overview of ICT

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. 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 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.



Preparation for ICT

  • No special preparation required

Sample Type for ICT

The sample type collected for Coombs Test - Indirect is: Blood

Interpreting ICT results

Interpretations

Agglutination: Positive result, antibodies present

No agglutination: Negative result, antibodies absent



Result

Interpretation

Negative

No antibodies detected

Equivocal

Positive in undiluted serum up to 1:16 titre

Positive

Positive in titre of 1:32 or above

Positive in increasing titre in subsequent tests


Antibodies are produced in the blood upon exposure to incompatible antigens as during a blood transfusion. Antibodies produced in the first incompatible transfusion produce severe reactions upon subsequent transfusions of the same blood type.


Answers to Patient Concerns & Frequently Asked Questions (FAQs) about ICT

Frequently Asked Questions about Coombs Test - Indirect

Q. How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle is used to withdraw blood sample from a blood vessel in your arm, generally from the inner side of the elbow area. The doctor, nurse or the phlebotomist will tie an elastic band around your arm which will help the blood vessels to 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. The needle is then inserted into the blood vessel to collect the sample. You may feel a tiny pinprick during the procedure. Blood sample, once collected, is then sent to the laboratory.
Q. 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 needle prick.
Q. What is HDFN?
Hemolytic Disease of Fetus and Newborn or HDFN is a condition where the blood type of the fetus is incompatible with the blood type of the mother. The most severe reactions typically occur due to Rh incompatibility, where antibodies are produced in the Rh negative mother against Rh positive fetus. These antibodies cross the placenta and react with the RBC of the fetus, causing HDFN.
Q. What other tests can be prescribed by your doctor in case of abnormal Indirect Coombs test result?
Additional test that may be prescribed in case of abnormal Indirect Coombs Test result is Antibody Identification Test. It helps to determine which antibodies are present in the sample that are causing an incompatibility reaction.
Q. What else can the Indirect Coombs Test be used for?
The Indirect Coombs Test can also be used to help diagnose the cause of hemolytic anemia due to autoimmune conditions. In an autoimmune disorder, antibodies are produced against the body’s own RBCs which attack and destroy the RBCs causing hemolytic anemia. Autoimmune hemolytic anemia can be caused by autoimmune diseases like Systemic Lupus Erythematosus, mycoplasma pneumonia infections, or certain cancers like lymphocytic leukemia and lymphoma.
Q. What is the difference between Indirect and Direct Coombs Tests?
Both Indirect and Direct Coombs Test are performed to determine the presence of anti-human RBC antibodies directed against human RBC antigens found on the RBCs. The Indirect Coombs Test is performed to determine antibodies produced against incompatible RBCs obtained from outside the body (as during a blood transfusion or during pregnancy). Whereas, the Direct Coombs Test is performed to detect the presence of antibodies directed against the patient’s own RBCs, which occurs during autoimmune diseases. Also, antibodies detected by the Indirect Coombs Test are present in the serum, while those detected by the Direct Coombs Test are attached to the surface of the RBCs. The Direct Coombs Test is performed to confirm if hemolytic anemia is being caused due to autoimmune disorder. The Indirect Coombs Test is performed primarily to determine compatibility of blood transfusion, or to check for Rh compatibility between a pregnant woman and her child before or during pregnancy.
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Provided By

NABL

CAP

About SRL Limited

For over a hundred years, human pathology has been one of the keystones of medicine and rightly so at SRL, we offer our patients world-class Pathology services because their well-being is of the utmost importance to us. Pathology is quite simply the scientific study of the overall response of your body to any foreign influence, i.e., disease. Actually, we use this knowledge to diagnose & subsequently treat your ailment. What we basically do is carefully compare the normal structure and function of a human body (anatomy and physiology) to the abnormal structure and function we witness in an unwell human. Doing this is the most crucial phase & we take note of even the minutest details while adjudging the extent of your ailment because one slip can lead to an incorrect diagnosis, posing serious threat to your health. Our experts ensure that they are extremely careful while analyzing the samples. This is where our advanced technology chips in. SRL is proud to host state-of-the-art equipments based on the latest technology for a speedy and accurate result. We do not take any chances whatsoever with your health & well-being. Avail our Pathology services with no hesitation. You are always in good hands with SRL.

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