This laboratory test is performed on a blood sample to detect antibodies or anti-globulins that are reactive against red blood cells. This is an abnormal function of antibodies. Normally, antibodies are proteins that react against harmful objects in the body. Direct coombs test detects the antibodies attached to the surface of red blood cells.
Why is this test performed?
This test is performed to:
Diagnose the cause of red blood cell destruction
To investigate the blood transfusion reaction
To detect the presence of mother antibodies against the fetus that cause hemolytic disease of the new born.
Collecting sample: A healthcare professional will collect blood from your vein into a test tube or from the heel stick, in the case of infants.
The sample is sent to the laboratory for analysis.
What is the difference between direct and indirect coombs test?
There are two types of coombs test:
Direct coombs test
Indirect coombs test
Direct coombs test detects the presence of antibodies reactive against RBCs stuck to the surface of RBCs while indirect coombs test detects the presence of antibodies roaming freely in the serum.
What are the causes of a positive coombs test?
A positive direct coombs test may be due to:
Incompatible blood transfusion
Hemolytic disease of the newborn
Medicines such as penicillin.
What are the symptoms of blood transfusion reaction?
Following are the symptoms after an incompatible blood transfusion:
What are the symptoms of HDN (hemolytic disease of newborn)?
Following are the symptoms of HDN:
Enlarged liver or spleen
Swelling in the whole body.
How to prepare for this test?
No special preparations are required for this test. However, inform your doctor about your complete medical history.
Interpretation of test results:
Negative: A negative direct coombs test means that there are no antibodies attached to the surface of red blood cells
Positive: A positive direct coombs test means that there are antibodies present on the surface of red blood cells; reactive to them.
You should get tested:
If you have symptoms that indicate a blood disease
If you are having symptoms of blood transfusion reaction
If a newborn is having symptoms of hemolytic disease of the newborn.