Competitive Immunoassay
An analytical method where the analyte competes with a labeled antigen for binding sites on a limited number of antibodies.
Full Definition
A competitive immunoassay is a laboratory technique used in hormone testing where the hormone of interest (analyte) competes with a known amount of labeled hormone for a limited number of binding sites on specific antibodies. As the concentration of the unlabeled hormone increases, less labeled hormone can bind, resulting in an inverse relationship between signal and analyte concentration. This method is particularly useful for measuring small molecules like steroid hormones (testosterone, cortisol, estradiol) that may not have multiple epitopes for sandwich assays. The technique requires careful optimization to ensure accurate quantification across the physiological range.
In Context
- "Cortisol measurement utilizes a competitive immunoassay format due to the hormone's small molecular size." — Method validation document
- "The competitive immunoassay showed good precision across the clinically relevant range for estradiol." — Quality control report