ELISA

ELISA refers to “enzyme-linked immunosorbent assay.” It is a serological test to check the presence of particular antigen/antibody.

There are variations of the ELISA test, but the most basic type consists of an antibody attached to a solid surface. This antibody has affinity for the substance of interest, for example, Human Chorionic Gonadotropin (HCG), the commonly measured protein which indicates pregnancy.

• An ELISA test uses components of the immune system and chemicals to detect immune responses in the body (for example, to infectious microbes).
• The ELISA test involves an enzyme (a protein that catalyses a biochemical reaction).
• It also involves an antibody or antigen (immunologic molecules).

A mixture of purified HCG linked (coupled) to an enzyme and the test sample (blood, urine, etc) are added to the test system. If no HCG is present in the test sample, then only HCG with linked enzyme will bind. The more HCG which is present in the test sample, the less enzyme linked HCG will bind. The substance the enzyme acts on is then added, and the amount of product measured in some way, such as a change in color of the solution.

ELISA tests are generally relatively accurate tests. They are considered highly sensitive and specific and compare favourably with other methods used to detect substances in the body, such as radio immune assay (RIA) tests. They have the added advantages of not needing radioisotopes (radioactive substances) or a costly radiation counter (a radiation-counting apparatus). They are basically of two types Direct Elisa Test (detecting antigens with the help of antibodies) and Indirect Elisa (to detect presence of specific antibody in a specimen such as Serum. It can be used to check various types of medical check up like HIV AIDS, Allergy, Hypothyroidism, Pregnancy etc.