Since the 1970s, most radioimmunoassays have been replaced by ELISA assays or enzyme-linked immunosorbent assays. ELISA is a frequently used technique in labs that measures the concentration of antigens or antibodies found in a particular solution. ELISA is set apart from its counterparts, as it can provide quantitative results and because the separation of specific and non-specific interactions happens during serial binding to the polystyrene multi-well plate, or another solid surface.
When the ELISA test is complete, it results in a finished product that is colored and will correlate to how much antigen or antibody is found in the original sample. ELISAs are a rapid and easy way to determine certain results and are often use as a first choice for research and diagnostic projects.
Currently, ELISAs have all but replaced radioimmunoassays. They can be used with variations and expanded formats to achieve different results and find different pieces of information. Multiple antigens or antibodies can be used per well and direct cell-based output can be determined.
Once completed, the ELISA assay test will produce three different types of results:
When determining quantitative results, the data received will be interpreted in comparison to a standard curve. This produces accurate calculations of the concentration of antigens in different samples.
Sometimes, the test results simply need to be a yes or a no. ELISA assays can give these answers, which tell the lab if a particular agent is present in a sample. With qualitative results, the sample is compared to a blank well that does not contain an antigen or an unrelated control antigen.
With semi-quantitative results, relative levels of antigen in the assay samples are compared. This works because the intensity of the signal will be different with each antigen concentration.
The data from ELISA is usually graphed with an optical density log and log concentration. This produces a sigmoidal curve. The standard curve on the graph is found by using known concentrations of an antigen. This curve is then utilized to measure the unknown sample concentration and compare it to the linear part of the standard curve. The graphing is often created with curve fitting software.