Specific binding assays employing label analog to reduce sample interferences

Claim 1

In a homogeneous apoenzyme reactivation immunoassay method for determining an analyte in a test sample suspected to contain a potentially interfering binding substance, wherein the test sample is combined with a reagent system that includes (i) a labeled reagent comprising a flavin adenine dinucleotide (FAD) label portion and a specific binding portion comprising the analyte or a binding analog thereof, (ii) an antibody capable of binding the analyte, and (iii) apoglucose oxidase, thereby forming a reaction mixture comprising an antibody bound-species and a free-species of the FAD-labeled reagent, the ability of the FAD-label portion of the labeled reagent to combine with the apoglucose oxidase to produce the catalytically active holoenzyme glucose oxidase being measurably different when the FAD-labeled reagent is in said bound-species compared to when in said free-species, said potentially interfering binding substance being capable of binding with the FAD-labeled portion of the labeled reagent; and wherein the glucose oxidase activity in the reaction mixture is measured and related to the amount of analyte in the test sample; the improvement which comprises adding to the reaction mixture a flavin structural analog of FAD which does not significantly combine with apoglucose oxidase to produce active glucose oxidase but which binds with the potentially interfering FAD-binding substance.