ENZYME-LINKED IMMUNOSORBENT ASSAY

The enzyme-linked immunosorbent assay is a commonly used analytical biochemistry assay, first described by Engvall and Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay to detect the presence of a ligand in a liquid sample using antibodies directed against the protein to be measured.

It is commonly used to measure antibodies, antigens, proteins and glycoproteins in biological samples. Some examples include: diagnosis of HIV infection, pregnancy tests, and measurement of cytokines or soluble receptors in cell supernatant or serum.

A positive ELISA test is always followed by a Western blot test. A positive Western blot confirms an HIV infection. A negative Western blot test means the ELISA test was a false positive test. The Western blot test can also be unclear, in which case more testing is done. Negative tests do not rule out HIV infection.

ELISA can be divided into four major types: direct, indirect, sandwich, and competitive.

1. Antibody coating. Specific capture antibody is immobilized on high protein-binding plates by overnight incubation.
2. Protein capture. Samples and standard dilutions are added to the wells and will be captured by the bound antibodies.
3. Detection antibody.
4. Streptavidin-enzyme conjugate.
5. Addition of substrate.
6. Analysis.

Depending on what the test is being used for, you may get results as quickly as about 24 hours if the test is done locally. However, there are some tests that may take days to weeks.

It is a plate-based assay technique designed for detecting and quantifying soluble substances such as peptides, proteins, antibodies, and hormones. Other names, such as enzyme immunoassay (EIA), are also used to describe the same technology.

This test can be used to determine if you have antibodies related to certain infectious conditions. Antibodies are proteins that your body produces in response to harmful substances called antigens. An ELISA test may be used to diagnose: HIV, which causes AIDS.

Because the ELISA test is extremely sensitive, some people may test falsely positive. Other infections such as lupus, Lyme disease, and other STDs may cause a false positive for HIV on the ELISA test. Because of this, positive ELISA test results need to be confirmed through another test.

The Western blot test separates the blood proteins and detects the specific proteins (called HIV antibodies) that indicate an HIV infection. The Western blot is used to confirm a positive ELISA, and the combined tests are 99.9% accurate.

ELISA has a number of benefits compared to the other immunoassay techniques. It is often preferred because it has high sensitivity and specificity. ELISA also offers more accuracy compared to other techniques such as radioimmunoassay (RIA) tests. ELISA assays are usually in 96 well microplate format.

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Regards,
Nicola B
Editorial Team
Journal of  Biochemistry and Biotechnology