Procedure and Types of Antiglobulin Test or Coomb's Test

Submitted on March 27, 2012

The Immune System and the Antiglobulin Test

The immune system is responsible for keeping the body healthy by keeping infection and illness at bay. The immune system produces a protein, known as antibodies, to protect the body. These antibodies attach themselves to invading particles like bacteria and viruses. Once they are bound to the offending particle, it proceeds to attack and destroy the foreign elements, keeping the body safe from illness.

While the antibodies are designed to protect the body, sometimes these antibodies turn against the body and attack and destroy healthy red cells instead. The impact of weakening red blood cells causes severe health complications. In such a case, an antiglobulin test is recommended.

An antiglobulin test, also known as Coomb’s test, is a lab test undertaken to identify and assert the presence of such rebel antibodies that attach themselves to red blood cells in the body and attack them. This test is also known as the anti-human globulin test. An antiglobulin test is essential to diagnose autoimmune disorders like lupus, anaemia and jaundice. It can also be used to verify blood type.


The antiglobulin test procedure is similar to a simple blood test. A blood sample is drawn from the vein, usually along the arm, and collected. From there on the sample is send to the lab to be tested. There it is examined for clumping together of cells as this indicates the presence of antibodies in the blood.

Types of Antiglobulin Testing

There are two types of antiglobulin tests – the direct antiglobulin test and the indirect antiglobulin test.

  • The direct antiglobulin test discovers antibodies in the red blood cells. It is used to determine the cause for conditions like anaemia, a condition wherein the red blood cells are destroyed faster than the body is able to produce.
  • The indirect antiglobulin test searches for the red blood cell attacking antibodies flowing in the blood serum. This liquid is pale and yellowish in appearance; it is what is left over after the red blood cells and the clotting particles are separated. This procedure is a rare one; it is mostly used to determine if a person is bound to have a negative reaction to blood transfusions.

Another case of testing may arise as part of prenatal testing in the case of partners with opposing blood types (Rh positive and negative, for example). In such a case if the mother and the baby have opposing blood types, the mother’s immune system could attack the foetus.