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Review the information below and explain to your patient with suspected Haemolytic Anaemia about their upcoming Coombs' Test.
What is a Coombs' test?
The two types of Coombs' test are as follows:
The direct Coombs' test involves looking directly at red blood cells found in a sample of blood. The direct Coombs' test is sometimes called the direct antiglobulin test (DAT).
The indirect Coombs' test looks at the liquid part of the blood (the plasma). The indirect Coombs' test is sometimes called the indirect antiglobulin test (IAT).
Both types of Coombs' test are looking for antibodies which may attack red blood cells and lead to them being destroyed.
What is a Coombs' test used for?
The direct Coombs' test may be used if doctors suspect a person is affected by a type of anaemia called haemolytic anaemia. Haemolytic anaemia is a condition where there are not enough red blood cells in the body because something in the body is destroying them. The Coomb's test is done to see if it is the immune system that could be causing the red blood cells to be destroyed.
The indirect Coombs' test is used to make sure that blood that has been donated is compatible with the patient who is going to receive it. It is also used to check that a pregnant mother's blood does not contain antibodies that might cause her baby harm. See the separate leaflet called Blood Tests.
How does a Coombs' test work?
Your red blood cells have certain proteins on their surface, called antigens. Also, your plasma contains a special type of protein called antibodies, which will attack certain antigens if they are present.
In a direct Coombs' test a special antibody is added to a sample of blood. This test checks whether there are antibodies that have already attached themselves to the surface of the red blood cell. If the antibodies that are added bind to the antibodies on the surface of the cell the test is positive. This causes the red blood cells to clump together in the test tube. A positive test shows that part of the immune system is causing red cells to be destroyed.
The indirect Coombs' test is done on a sample of the liquid part of the blood. It looks for antibodies in the bloodstream that aren't attached to the red blood cells but could bind to certain red blood cells and destroy them.
What happens during a Coombs' test?
A Coombs' test involves taking a sample of blood. The blood sample is then sent to the laboratory where the Coombs' test is carried out.