Summary

The Direct Antiglobulin Test (DAT) is performed if your doctor suspects that the cause of your symptoms is due to your red cells being destroyed by antibodies. This can occur as part of an abnormal reaction to a blood transfusion, or it can be due to an autoimmune disease. It can also occur in babies with haemolytic disease of the foetus and newborn (HDFN). The DAT shows whether antibodies are attached to the red blood cells and if they are, what type of antibody is destroying the cells.

Why get tested?

Antigens are molecules found on the surface of red blood cells. They are inherited from your parents and the type you have determines your blood type. The basis of how blood is classified in groups according to the antigens on your blood cells is explained in the Test called Blood Group.

Red blood cells have a lifespan of about 120 days. Your body must be constantly making new ones as the old ones die off. Some autoimmune diseases like lupus cause your immune system to attack and destroy red blood cells. This can also occur in some types of blood transfusion reactions and in some reactions to medications.

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.

As red cells break down, a chemical called bilirubin is released which makes the skin and the whites of eyes go yellow, a sign known as jaundice.

Having the test

Sample
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).

Any preparation?

None

Your results

The results of the test are reported as negative or positive. The degree of positivity and the type of antibody present may also be reported.

A positive DAT indicates you have antibodies on your red cells which could be the cause of the red cell destruction. The stronger the degree of positivity the larger the amount of antibody on the red cells. The type of antibody can help in diagnosing the cause of red cell destruction.  

Treatment of the cause will vary, but in the case of HDFN, the condition needs to be monitored and treated to prevent possible complications.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms.   It is important that you tell them everything you think might help. 

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely. 

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Any more to know?

A positive DAT in the case of a transfusion reaction or due to a medication can remain positive for days to months, whereas in someone with an autoimmune condition, the test may stay positive for longer.

More information

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