Methods and kits are provided for the simultaneous detection of multiple analytes, i.e. to the determination of whether one or more of a plurality of analytes is present in a sample, particularly the plurality of analytes are structurally unrelated or significantly different, particularly to whether one or more of such analytes is present in a sample in a concentration that is above a predetermined minimum or cutoff value, and particularly for such analytes with different cutoffs. The methods and kits are particularly useful for-screening for the presence of a plurality of drugs (licit and/or illicit), performance-enhancing substances, and other chemicals, and involve a competitive enzyme immunoassay employing one or more conjugates of G6PDH with a plurality of the analytes.