Methods and reagents are disclosed for detecting a false result in an assay measurement for determining a concentration of an analyte in a sample suspected of containing the analyte. The method comprises measuring assay signal resulting from background only and measuring assay signal resulting from the presence of analyte in the sample plus background and subtracting the first measurement from the second measurement to determine the concentration of analyte in the sample. For example, a measurement result 1 is determined by means of an assay conducted on a portion of the sample where analyte in the sample is substantially sequestered and a measurement result 2 is determined by means of the assay conducted on an equal portion of the same sample where analyte in the sample is substantially non-sequestered. Measurement result 1 is subtracted from measurement result 2 to determine the concentration of analyte in the sample.