At a glance

Also known as

Direct Coomb’s test; Coomb’s test; DAT; DCT; DC

Why get tested?

To screen and monitor diseases or conditions that result in destruction of red blood cells such as haemolytic anaemia, transfusion reactions and haemolytic disease of the newborn (HDN).

When to get tested?

If your doctor suspects that your immune system may be destroying your red blood cells. This may be indicated by anaemia (low haemoglobin or red cell count), small red blood cells (microcytic anaemia) and other signs of red blood cell destruction.

In newborn babies this can occur due to antibodies from the mother attacking the baby’s red blood cells either before, or immediately after, birth.

Sample required?

The direct antiglobulin test is performed on a blood sample taken by a needle placed in a vein in the arm or by a finger-prick (for children and adults) or heel-prick (for infants).

Test preparation needed?

None

What is being tested?

Red blood cells have chemical structures (most commonly proteins or carbohydrates) on the outside surface. These chemical structures usually have a defined function such as determining the shape of the cell or the transport of chemicals into, or out of, the red blood cell. In addition, they determine our blood group. There are over 200 different blood groups known.

Our immune system is very good at recognising foreign particles that may be harmful to us. Occasionally however this gets mixed up and our immune system recognises parts of our own body as being foreign, and then tries to destroy them. This group of diseases are known as autoimmune diseases, and include a range of conditions including some forms of arthritis.

Some autoimmune diseases attack and destroy red blood cells. This results in anaemia and in some cases may be life threatening. A similar situation occurs in some types of transfusion reactions. In pregnancy, red blood cell antibodies can cross the placenta and enter the baby’s bloodstream. These can destroy the baby’s red blood cells resulting in anaemia. As they break down they release bilirubin, resulting in jaundice. This needs to be treated promptly to prevent complications, and even death, of the baby.

This test tells the doctor whether red blood cell antibodies are attached to the red blood cells and, if they are, what type of antibody it is. This can be used to assist and monitor treatment.

How is the sample collected for testing?

The direct antiglobulin test is performed on a blood sample taken by a needle placed in a vein in the arm or by a finger-prick (for children and adults) or heel-prick (for infants).

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

The direct antiglobulin test tells the doctor whether red blood cell antibodies are attached to the red blood cells and, if they are, what type of antibody it is. This can be used to assist and monitor treatment.

When is it requested?

When the doctor suspects an autoimmune disease that can attack and destroy red blood cells. The test may help with diagnosis of the disease or may be used to monitor treatment.

It is also used in cases of suspected transfusion reactions and to help diagnose haemolytic disease of the newborn.

What does the test result mean?

Looking for reference ranges?

A positive test result means that red blood cell antibodies are attached to the red blood cell. This can be used to diagnose and monitor the disease.

Common Questions

What are the risks of a transfusion?

Transfusion is associated with a number of risks. You should make the decision as to whether a transfusion is required in consultation with your doctor and with an understanding of these risks. More information regarding risks can be found in Feature: Blood banking risks and Australian Red Cross Blood Service: Transfusion medicine.

Last Review Date: December 6, 2014