Direct Coombs Test- Why am I having this test?
Direct Coombs test, also called the direct antiglobulin test (DAT), is done to identify immune hemolysis. This is a condition in which antibodies form and attack the red blood cells (RBCs). Immune hemolysis can lead to anemia (hemolytic anemia). This test is commonly used to confirm a transfusion reaction.
Your health care provider may perform this test if hemolytic anemia is suspected, or if you experience the following symptoms after a blood transfusion:
- Fever.
- Chills.
- Rash.
- Side (flank) or back pain.
- Blood in your urine.
- Fainting or dizziness.
What is being tested?
The test looks for antibodies that are attached to your RBCs. Antibodies may attach to your RBCs after a blood transfusion if your body recognizes that the blood is not your own. Your body could then produce antibodies against those foreign blood cells. In this situation, antibodies could attach to the RBCs and result in their destruction.
What kind of sample is taken?
A blood sample is required for this test. It is usually collected by inserting a needle into a blood vessel. In newborns, blood may be taken from the umbilical cord.
How are the results reported?
Your test results will be reported as either positive or negative. For this test, a normal result is:
- Negative, no agglutination.
A false-positive result can occur. A false positive is an error in the test result that reports that a condition is present when it is not. Causes of a false positive may include:
- Medicines such as insulin, certain antibiotics, and drugs used to treat Parkinson’s disease.
- Certain antibodies in the blood (antiphospholipid antibodies).
A false-negative result can occur. A false negative is an error in the test result that reports that a condition is not present when it is.
What do the results mean?
Results other than “negative, no agglutination” may indicate:
- A blood disorder (hemolytic disease) of a newborn.
- An incompatible blood transfusion reaction.
- Lymphoma.
- Certain types of hemolytic anemia.
- Certain infections.
Talk with your health care provider about what your results mean.
Questions to ask your health care provider
Ask your health care provider, or the department that is doing the test:
- When will my results be ready?
- How will I get my results?
- What are my treatment options?
- What other tests do I need?
- What are my next steps?
Summary
- The direct Coombs test, also called the direct antiglobulin test (DAT), is performed to identify a condition in which antibodies form and attack red blood cells in the body (immune hemolysis).
- This test is ordered if hemolytic anemia is suspected, or if you experience certain reactions after a blood transfusion.
- Your results will be reported as positive or negative. Talk with your health care provider about what your results mean.
