A2_6 Free Analyte Immunoassay

Free Analyte Immunoassay is a special family of assay formats, designed to measure free analyte in blood samples, i.e., the fraction that is not bound to carrier protein. This is important if the free analyte is the metabolically active fraction. Free thyroxine is the most well known example. The free fraction is just 0.02% of the total. This chapter explains how this can be measured independently.

This chapter explains the clinical significance and importance of free hormone concentrations. Starting from the basic principles, formulae are developed to measure the impact of different binding proteins on free hormone concentration, using thyroxine as an example. A spreadsheet model is provided that calculates free hormone concentration and allows predictions to be made across a wide range of clinical situations. Using the spreadsheet various scenarios are investigated and relationships explored. Different types of free hormone assay format are reviewed, with their limitations. Finally there is a section on validation of free hormone assays, which requires special methodology.

Nic Christofides. Having worked in academia for 11 years (at the Imperial with Sir Stephen Bloom) and 22 years in industry (Ortho Clinical Diagnostics Scientific) Nic is currently working as a scientific consultant. This entails advising customers (small and large companies) on all aspects of immunoassay development, including R&D, validation, trouble-shooting and helping with promotional materials, e.g. publications.