Direct antiglobulin test (DAT / direct Coombs)
A test that detects whether red blood cells are coated with antibodies. Its main use is to find out whether an anaemia is caused by the immune system attacking the red cells — autoimmune haemolytic anaemia — and to investigate transfusion reactions and haemolytic disease of the newborn.
What it measures
The direct antiglobulin test, also called the direct Coombs test, checks whether red blood cells are coated with antibodies (or complement proteins) on their surface. It works by adding a reagent that clumps together any cells that are antibody-coated, and the result is reported as negative or positive. Its purpose is specific: to determine whether a haemolytic anaemia — one in which red cells are being destroyed prematurely — is immune-mediated. When the body's own immune system produces antibodies against its red cells, they become coated and are removed early, causing autoimmune haemolytic anaemia; the DAT is the test that confirms this immune mechanism. It is also central to investigating a transfusion reaction (where antibodies attack transfused cells) and haemolytic disease of the newborn (where maternal antibodies cross to the baby). A positive DAT points to an immune cause of red-cell destruction and directs the search for a trigger — an underlying autoimmune disease, certain infections, some cancers, or a drug. A negative result in the setting of haemolysis points instead to non-immune causes.
What a high value can mean
- A positive DAT indicates antibody-coated red cells — an immune cause of red-cell destruction.
- Autoimmune haemolytic anaemia — the classic reason for a positive result.
- A transfusion reaction — antibodies against transfused red cells.
- Haemolytic disease of the newborn — maternal antibodies against the baby's cells.
- Drug-induced immune haemolysis, and sometimes an underlying autoimmune disease, infection or blood cancer.
High Direct antiglobulin test (DAT / direct Coombs): full guide
What a low value can mean
- A negative DAT — no detectable antibody coating; if there is haemolysis, it points to a non-immune cause (such as a mechanical, hereditary or enzyme problem like G6PD deficiency).
- A negative result is the expected finding in most people without immune red-cell destruction.
Low Direct antiglobulin test (DAT / direct Coombs): full guide
When to discuss with a doctor
The direct antiglobulin test is a specialist test used within the investigation of haemolytic anaemia and transfusion medicine, not a routine screen. It is ordered when there are signs that red cells are being destroyed — such as anaemia with a high reticulocyte count, a low haptoglobin, a raised LDH and jaundice — to determine whether the immune system is the cause. A positive result establishes an immune mechanism and leads to a search for the underlying trigger and appropriate treatment; a negative one redirects the workup toward non-immune causes. Because it is interpreted within a full haemolysis workup by a doctor, and often by haematology, the result is understood in that context. Mediora.AI can show the DAT alongside the haemolysis markers (haptoglobin, reticulocytes, LDH, bilirubin) so the pattern is read together; the interpretation belongs with your doctor.