Coomb’s Test- Direct and Indirect Coomb’s Test


Coomb’s test, also known as antiglobulin test, is a blood test that detects the presence of antibodies or complement proteins that are bound to the surface of red blood cells (RBCs). These antibodies or complement proteins can cause the RBCs to be destroyed by the immune system, leading to a condition called hemolysis. Hemolysis can result in anemia, jaundice, and other complications.

The main objective of Coomb’s test is to diagnose and monitor hemolytic diseases, such as autoimmune hemolytic anemia, hemolytic disease of the newborn, transfusion reactions, and drug-induced hemolysis. Coomb’s test can also be used to identify certain infections and autoimmune disorders that can cause RBC sensitization.

Coomb’s test is based on the principle that antibodies or complement proteins attached to the RBCs can be detected by adding a reagent called anti-human globulin (AHG), which is an antibody that binds to human antibodies or complement proteins. The AHG causes the sensitized RBCs to clump together (agglutinate), which can be observed under a microscope or by visual inspection.

There are two types of Coomb’s test: direct and indirect. The direct Coomb’s test checks for antibodies or complement proteins that are already attached to the patient’s RBCs in vivo (in the bloodstream). The indirect Coomb’s test checks for antibodies that are floating in the patient’s serum and can attach to RBCs in vitro (in the laboratory).

In this article, we will explain the principle, procedure, interpretation, applications, and limitations of both types of Coomb’s test. We will also provide some examples of medical conditions that can be diagnosed or monitored by Coomb’s test.