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 Direct Antiglobulin Test shows whether antibodies are attached to the red blood cells and if they are, what type of antibody is destroying the cells.
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 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 result mean?
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
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 on the Australian Red Cross Blood Service: Transfusion medicine website.
More information
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