Direct Coombs Test (Direct Antiglobulin Test)

Antibodies attacking red cells

The direct Coombs test, also called the direct antiglobulin test (DAT), checks whether antibodies or immune proteins are stuck to the surface of your red blood cells. When this happens, the body can destroy red cells early, a process called haemolysis, which can lead to anaemia and jaundice. Doctors use it to find an immune cause of red-cell breakdown, such as autoimmune haemolytic anaemia, a reaction to a blood transfusion, or haemolytic disease of the newborn.

• To investigate anaemia with signs of red-cell breakdown, such as jaundice or dark urine
• When a reaction to a recent blood transfusion is suspected
• To check a newborn baby with jaundice when the mother's and baby's blood groups differ
• When a medicine or an autoimmune condition is thought to be attacking red cells

You do not need to fast or change your routine. Tell the collector about any blood transfusion in recent months, any current pregnancy, and the medicines you take, because some medicines can cause a positive result. Keep taking your usual medicines unless your doctor advises otherwise.

Sample

Blood sample

How it works

A trained collector visits your home and draws a small amount of blood from a vein in your arm. The tube is labelled with your details and sent to the laboratory. The draw itself usually takes a few minutes.

Report

Within 24 hours of collection.

A negative result means no antibodies were found on your red cells. A positive result means antibodies or immune proteins are attached, which can be due to an autoimmune condition, a transfusion reaction, some medicines, certain infections or, in babies, antibodies from the mother. Some people have a positive result without any red-cell breakdown. Your doctor will interpret it together with tests such as a CBC, reticulocyte count and bilirubin.

One test: Direct Coombs Test (Direct Antiglobulin Test), from one blood sample.