Quantitative, Qualitative, Semi-quantitative
The ELISA assay yields three different types of data output:
ELISA data can be interpreted in comparison to a standard curve (a serial dilution of a known, purified antigen) in order to precisely calculate the concentrations of antigen in various samples.
ELISAs can also be used to achieve a yes or no answer indicating whether a particular antigen is present in a sample, as compared to a blank well containing no antigen or an unrelated control antigen.
ELISAs can be used to compare the relative levels of antigen in assay samples, since the intensity of signal will vary directly with antigen concentration.
ELISA data is typically graphed with optical density vs log concentration to produce a sigmoidal curve as shown in Figure 8. Known concentrations of antigen are used to produce a standard curve and then this data is used to measure the concentration of unknown samples by comparison to the linear portion of the standard curve. This can be done directly on the graph or with curve fitting software which is typically found on ELISA plate readers.
Figure 8. A typical ELISA standard curve.
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