Coombs test

Coombs test
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Purpose	Detects antibodies that act against the surface of red blood cells
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The Coombs test, also known as the antiglobulin test, is a clinical blood test used to detect antibodies that may bind to the surface of red blood cells (RBCs). It is primarily used in the diagnosis of hemolytic anemia, hemolytic disease of the newborn, and in blood transfusion compatibility testing.

Types of Coombs Test

There are two main types of Coombs tests:

Direct Coombs Test

The Direct Coombs Test (DCT), also known as the Direct Antiglobulin Test (DAT), is used to detect antibodies or complement proteins that are bound to the surface of red blood cells. This test is commonly used to diagnose conditions such as autoimmune hemolytic anemia and hemolytic disease of the newborn.

Algorithm in positive direct antiglobulin test

Indirect Coombs Test

The Indirect Coombs Test (ICT) is used to detect antibodies that are present in the serum and are capable of binding to red blood cells. This test is often used in prenatal testing of pregnant women and in testing blood prior to transfusion.

Procedure

The Coombs test involves the following steps:

1. Sample Collection: A blood sample is collected from the patient. 2. Addition of Coombs Reagent: The Coombs reagent, which contains anti-human globulin, is added to the blood sample. 3. Observation for Agglutination: The sample is observed for agglutination (clumping) of red blood cells, which indicates a positive result.

Clinical Significance

The Coombs test is significant in several clinical scenarios:

• Autoimmune Hemolytic Anemia: The direct Coombs test can confirm the presence of antibodies that are causing the destruction of red blood cells.
• Hemolytic Disease of the Newborn: The test can detect antibodies in the mother that may attack the red blood cells of the fetus.
• Blood Transfusion: The indirect Coombs test is used to screen for antibodies in the recipient's serum that may react with donor red blood cells.

Limitations

While the Coombs test is a valuable diagnostic tool, it has limitations. False positives can occur due to non-specific binding, and false negatives may occur if the antibody levels are too low to detect.

Also see

• Hemolytic anemia
• Blood transfusion
• Hemolytic disease of the newborn
• Autoimmune disease