Enzyme-Linked Immunosorbant Assay, or ELISA, is a quantitative assay that uses antibodies to determine the amount of a substance (usually a protein) within a sample. The amount of protein is then quantified using a reporter tag that is attached to the antibody. This reporter is most often a color change driven by an enzyme attached to the antibody.

Three types of ELISA are typically used:
1. Direct ELISA - One-step method. This method uses one antibody specific for the protein of interest that is also attached to the reporter tag.

2. Indirect ELISA - Two-step method. This method is more typically used over the direct method. Indirect ELISA uses an untagged antibody specific for the protein of interest (Primary Antibody) that is followed by a tagged antibody that is specific for the Primary Antibody. The Indirect ELISA is not as fast as the Direct ELISA method but the signal is amplified with the added Secondary Antibody step allowing detection of low abundance proteins.

3. Sandwich ELISA - Three (or four)-step method. This is the most sensitive method and is often used for ELISA-based protocols. This method starts with the antibody specific to the protein of interest bound to a substrate (usually a plastic dish). The solution containing the protein of interest is then added so the protein will bind to the antibody on the plate. The following steps are exactly as performed in the Direct ELISA or Indirect ELISA (described above).

The ELISA Assay is used for many different types of Blood Tests. For more information on different Blood Tests and how to Interpret Results Please Click: Blood test codes and results explained

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