ELISA is a laboratory test used to identify specific proteins and their concentrations in a sample, often blood, to test for exposure to infectious agents. The test is performed using a microwell plate and specific antigens, and can produce false positives.
The ELISA procedure is a procedure used to perform an enzyme immunosorbent array (ELISA), a test that can be used to identify the presence of specific proteins and determine their concentrations. There are actually several procedures that can be used for an ELISA test, including direct, indirect, and so-called “sandwich” procedures. In all cases, the ELISA procedure is performed in the laboratory under controlled conditions to minimize the risk of false results.
To conduct an ELISA test, you need to have a sample such as blood. A common reason for conducting an ELISA is to test for exposure to an infectious agent, in which case the sample in question may or may not have a specific protein, and the test is conducted to look for that protein. The test can also be used to check the concentration of a protein.
To conduct the test, a device called a microwell plate is often used. Fans of medical and crime dramas are probably familiar with microtiter plates; they look like small trays with multiple inserts, each of which holds a vial. In the sandwich ELISA procedure, the technician begins by coating the vials with a known antigen of a known concentration, then washing them with a buffer solution. Subsequently, a serum obtained from a patient sample washed in the same buffer solution is added.
If the patient already has antibodies to the antigens in the tubes, they will stick to the sides of the tubes. The next stage of the ELISA procedure involves introducing the same antigen, labeled with an enzyme, into the test tubes. The antigen locks onto the antibodies that have stuck to the sides of the tubes. The enzyme fluoresces or changes color, allowing the technician to see that the serum had antibodies that bind to the antigens, and to determine their concentration, based on the strength of the enzyme reaction.
An ELISA procedure is very sensitive and extremely accurate, with technicians using very specific antigens to make sure they are identifying the right antibodies, or vice versa, depending on the type of test being conducted. However, false positives do happen. In an example of a false positive, the ELISA test is commonly used to check for signs of HIV exposure and sometimes produces a false positive because the solution can bind to an HIV-associated protein that some people have without becoming infected. That’s why a positive needs to be confirmed with a Western Blot.
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