Direct antiglobulin test

The expected result is Negative; a positive result is usually graded (for example 1+ to 4+) and the laboratory often reports which antibody type (IgG or complement) is coating the cells.

The direct antiglobulin test looks for antibodies or complement proteins stuck to the surface of the red blood cells. When the immune system is attacking the red cells, they become coated in this way and are removed early by the spleen. The test gives a negative or positive answer, often with a strength grade.

Doctors request it when they are looking into whether red blood cells are being broken down by the immune system, after a blood transfusion reaction, in newborn jaundice, and in some autoimmune conditions and blood cancers.

• Autoimmune haemolytic anaemia, where the body makes antibodies against its own red cells
• A reaction to a blood transfusion
• Newborn jaundice caused by the mother's antibodies
• Some medicines, including some antibiotics and some used for cancer
• Some autoimmune conditions and blood cancers

• A negative result means no antibody coating was found at the level the test can detect

• A weakly positive result is found in a small number of healthy people and in some who have had transfusions, with no red cell breakdown
• Some medicines and some infections give a positive result without any harm to the red cells
• Immunoglobulin infusions can give a positive result for some weeks

No fasting needed. Read alongside the haemoglobin, reticulocytes, bilirubin, haptoglobin and blood film.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.