Application of sandwich immunoassays for the determination of sample-specific background signals and its use for calibration of immunoassays

Sample-related background signals in immunoassays can be measured by a variation of the double antibody sandwich principle, in which the unlabelled specific antibody is substituted by a similar unrelated no-specific antibody. This permits differentiation between the analyte-specific and the background signal components for each sample. The method permits selection of sera with no or low analyte content for use as analyte diluent and for defining the zero point of the calibration curve. The method also permits control of analyte content during production processes which may change the background signal as well as identification of samples with atypical background signals. The procedure has been used for the calibration of enzyme immunoassays for α-fetoprotein (AFP) and human thyroid-stimulating hormone (TSH).