CALIBRATION HETEROGENEOUS IMMUNOASSAY

An assay method and compositions are provided for determining the presence of an analyte in a sample. The analyte is a member of an immunological pair (mip) comprising ligand and receptor. By providing a first measurement surface capable of specifically binding a labelled reagent in an amount depending upon the presence of analyte in the sample and a second calibration surface capable of binding a second labeled reagent in a manner unaffected by the presence of analyte in the sample, calibration of individual tests can be accomplished simultaneously with the performance of the test itself. A signal producing system includes an enzyme, a catalyst usually bonded to a mip which defines the first labeled reagent for binding to the measurement surface and the same catalyst conjugated to a ligand capable of binding to the calibration surface. Preferably, both labeled reagents have the same composition and the calibration surface includes anti-(first catalyst).