The E. histolytica ELISA test is a qualitative enzyme immunoassay for the detection of antibodies to E. histolytica, in samples of human serum or plasma. This test is intended to be performed by trained medical technologists only. Amebiasis is the disease caused by the protozoan parasite Entamoeba histolytica. This organism is endemic throughout the world in developing countries, and can be found in immigrants and travelers from these areas. The disease usually manifests with intestinal symptoms. In a minority of cases, the organism will become extra-intestinal and lead to abscess formation in different organs. Of the organs that could be affected, the liver is the most common site. Typically, the organism can no longer be found in the feces once the disease goes extra-intestinal. Serological tests are useful in detecting infection by E. histolytica if the organism goes extra-intestinal and in excluding the organism from the diagnosis of other disorders (e.g. chronic liver diseases, ulcerative colitis, etc.). This serology test should not be used for detecting intestinal infections. An Ova & Parasite (O&P) test or an E. histolytica fecal antigen assay is the proper assay for intestinal infections. Since antibodies may persist for years after clinical cure, a positive serological result may not necessarily indicate an active infection. A negative serological result however can be equally important in excluding suspected tissue invasion by E. histolytica. The microwells are coated with E. histolytica antigen. During the first incubation with the diluted patients' sera, any antibodies which are reactive with the antigen will bind to the coated wells. After washing to remove the rest of the sample, the Enzyme Conjugate is added. If antibodies have been bound to the wells, the Enzyme Conjugate will then bind to these antibodies. After another series of washes, a chromogen (tetramethylbenzidine or TMB) is added. If the Enzyme Conjugate is present, the peroxidase will catalyze a reaction that consumes the peroxide and turns the chromogen from clear to blue. Addition of the Stop Solution ends the reaction and turns the blue color to a bright yellow color. The reaction may then be read visually or with an ELISA reader.