In an ELISA, what is typically measured to determine positive results?

In an ELISA (Enzyme-Linked Immunosorbent Assay), the primary measurement used to determine positive results is optical density. This technique involves the use of an enzyme-linked antibody that produces a color change upon reaction with a substrate. As the reaction occurs, the intensity of the color produced is proportional to the concentration of the target antigen or antibody present in the sample.

Optical density is measured using a spectrophotometer, which quantifies the amount of light absorbed by the solution at a specific wavelength. A higher optical density indicates a greater concentration of the target analyte, suggesting a positive result in the assay. Therefore, the detection of optical density is crucial for interpreting the presence and quantity of the specific biomolecule being tested.

Other measurement options such as pH levels, temperature changes, or volume changes are not typically utilized in the context of ELISA for determining positive results. They do not provide relevant quantitative data about the presence of antibodies or antigens in the sample, which is the essential function of an ELISA assay. Thus, optical density remains the standard parameter measured in this type of immunological test.