What does Fluorescence Polarization Immunoassay (FPIA) measure?

Fluorescence Polarization Immunoassay (FPIA) is a technique used to measure the concentration of substances, particularly analytes in biological samples, by assessing the modulation of light emission from a fluorophore-ligand complex. In FPIA, a fluorescent tracer is bound to a ligand, and when the ligand binds to its specific antibody, the rotation of the complex slows down, leading to a change in the polarization of the emitted fluorescent light. The degree of light polarization is inversely proportional to the concentration of the analyte: higher concentrations result in decreased polarization due to reduced rotation. This method is particularly useful for measuring small molecules, hormones, and drugs in various samples.

The other options do not accurately describe what FPIA measures. Heavy metals require different detection methods, pH levels are typically measured with pH meters or indicators, and blood cell counts involve hematological techniques such as automated analyzers and microscopy, rather than fluorescence techniques.