Coombs Test

Cold agglutinin disease (CAD) is a type of autoimmune hemolytic anemia (a group of blood disorders) in which the immune system mistakenly attacks red blood cells at low temperatures.

The Coomb’s test is one of the diagnostic tests for CAD.

About the Coomb’s test

In CAD, the immune system produces autoantibodies called cold agglutinins that mistakenly attack red blood cells upon exposure to cold temperatures. Cold agglutinins bind to the surface of the red blood cells, causing them to clump and triggering their premature breakdown.

The Coomb’s test can detect cold agglutinin antibodies in the blood. The test comes in two types, direct and indirect. The direct Coomb’s test detects antibodies and other immune system-related proteins that are attached to red blood cells. The indirect Coomb’s test detects free-floating autoantibodies such as cold-agglutinins in the serum, the liquid component of blood.

Before the test

No specific preparation is required before the test. However, a history of blood transfusion, pregnancy, and some medications such as insulin and certain antibiotics may interfere with test results or make the patient ineligible to take the test. Therefore, the healthcare team must be informed about any such conditions before the test.

During the test

During this simple procedure, a healthcare professional will use a needle to collect blood from a vein in the patient’s arm. The blood sample will then be processed to separate the red blood cells and the serum. If finding the vein is difficult, more than one needle pricks may be required.

After the test

The patient may get a bruise at the site of the needle prick, and feel sore. This should resolve on its own with time. In rare cases, the patient may experience phlebitis or swollen veins following sample collection. A warm compress can help soothe the veins and improve blood flow to the area.

Additional information

The Coomb’s test can also be used to diagnose several other conditions including systemic lupus erythematosus, other types of acquired autoimmune hemolytic anemia, leukemia, a hemolytic disease in a newborn, and syphilis. It is also used to determine compatibility before blood transfusions.


Last updated: Aug. 7, 2019


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