Abstract
We have evaluated the cross-reactivity characteristics of two distinct immunometric assays for the measurement of free β-human chorionic gonadotropin (free β). These maternal serum assays have been used in the initial studies which evaluated free β as a marker in the prenatal detection of Down's syndrome. It has been suggested that free β assays are subject to substantial potential for cross-reactivity. To confirm that free β was the analyte responsible for enhanced detection efficiency both non-competitive and competitive cross-reactivity evaluations were undertaken. These studies demonstrated acceptably small cross-reactivity to other glycoprotein hormones or their β components. We conclude that properly designed free β assays will provide specific analyte measurement and improved detection efficiency in Down's syndrome screening.