Abstract: Non-competitive immunoassays and kits for detecting or determining the concentration of an analyte in a biological sample are provided along with reagents for use in such assays and kits. Immunoassays are provided which employ a reagent containing an autologous analyte which raises the signal above the background noise caused by non-specific binding thereby lowering the percent coefficient of variation of a non-competitive assay. By employing an autologous analyte in a reagent of the immunoassay, low dosages of an analyte can be detected without adversely affecting the long linear range of the assay.