title: One-step immunoassays for free (unbound) hormones: the effect of tracer binding by serum proteins.
abstract: In binding assays for determination of free (non-protein-bound) hormones in serum or plasma, the influence of the measuring system on the original analyte concentration in the sample must be considered. In one- or single-step free-hormone immunoassays, the labeled analyte or analog-tracer not only is bound to the antibody, it also is bound, to some extent, to serum proteins. The dependence of the assay response on two unknown variables--the concentration of free analyte and the binding potential of serum for the tracer--introduces a bias between the actual (original) and measured hormone concentrations. The significance of this protein effect is described by mathematical modeling of the analyte-protein distribution in the assay system. The theoretical consideration is validated by a clearly defined one-step assay system for measurement of free-thyroxin concentration, with a labeled thyroxin-immunoglobulin conjugate used as tracer.
mesh_terms: D000915:Antibody Affinity; D001798:Blood Proteins / Q000032:analysis*; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007074:Immunoglobulin G / Q000032:analysis; D008433:Mathematics; D011485:Protein Binding; D013974:Thyroxine / Q000097:blood* / Q000276:immunology
chemical_list: D001798:Blood Proteins; D007074:Immunoglobulin G; D013974:Thyroxine