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What is an ELISA Test?

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  • Written By: Charity Delich
  • Edited By: Bronwyn Harris
  • Last Modified Date: 19 September 2016
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An enzyme-linked immunosorbent assay, or ELISA, test is a type of medical diagnostic test used to detect whether a certain antibody or antigen is present in a patient. It can be useful for a range of different purposes relating to immunology, such as disease testing and virus testing. For example, an ELISA HIV test may be administered to determine whether a patient has been infected with HIV antibodies. In addition, ELISA tests are sometimes also used in testing for illegal drug use. An ELISA test can also help detect allergic reactions to food products like nuts or dairy items.

During an ELISA procedure, a health care provider typically collects a blood sample from a patient. This is usually done by inserting a needle into a vein on the back of the patient’s hand or in the patient’s inner elbow area. Alternatively, an ELISA test may allow for a urine sample. In any case, the collected test sample is placed into a test tube or onto a test slide or strip. The health care provider then sends the sample to a laboratory for analysis.

At the laboratory, technicians will determine whether the targeted antibody or antigen is present in the test sample. If a patient has a certain disease or condition, his or her sample will contain antibodies for that disease or condition. These antibodies will latch on to antigens, which are used as bonding agents in most ELISA tests.

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The lab technician will clean the test sample using a special test solution that washes away everything but the antigens,or the antibodies that cling to the antigens. Next, the lab technician applies an enzyme solution to the test sample. If the sample changes colors or provides some other indication, the target antibody or antigen is present in the test sample and the patient will test positively for the condition.

In general, an ELISA test is considered reliable within the immunology community. It is possible, however, for a patient who does not actually have the targeted infection to experience a phenomenon known as a false positive. A false positive occurs when a patient who is not infected with the target antibodies gives a positive result during the ELISA test.

False positives can occur for several reasons. For instance, if a sample becomes contaminated or inadvertently switched in the laboratory, a false positive may result. Patients with hemophilia or hemodialysis, or alcoholic patients with hepatitis are also more susceptible to experiencing false positives. Injection drug users and women who have had multiple pregnancies can also be more likely to realize false positives.

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