The invention generally relates to methods for indicating whether an assay for isolating targets is properly isolating and detecting targets. Methods of the invention involve obtaining a sample suspected of a containing target, introducing a detectable marker into the sample, conducting an assay using magnet particles to isolate the detectable marker and the target if it is present in the sample, determining the presence or absence of the target; and confirming that the assay functioned properly by determining presence or absence of the detectable marker.