Methods, devices, and systems for analyzing biological samples for the presence of an analyte by an initial assay, and, contingent upon the results of the initial assay, by a subsequent assay are provided. A sample may be diluted. A portion of a sample may be retained for use in such a subsequent assay. Initial assay results may be used to determine, for example, one or more of: whether or not a subsequent assay is performed; which subsequent assay is performed; the method of performing a subsequent assay; the order of performance of a sequence of subsequent assays; the steps, or order of steps, performed in a subsequent assay; the timing of the performance of a subsequent assay; the choice of a reagent used in a subsequent assay; the detection method used in a subsequent assay; and other particulars of assays may be contingent on the results of a prior assay.