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A high-throughput prioritization method was developed for use with a validated confirmatory method detecting organophosphorus nerve agent exposure by immunomagnetic separation high-performance liquid chromatography tandem mass spectrometry. A ballistic gradient was incorporated into this analytical method to profile unadducted butyrylcholinesterase (BChE) in clinical samples. With Zhang et al.’s Z′ factor of 0.88 ± 0.01 (SD) of control analytes and Z factor of 0.25 ± 0.06 (SD) of serum samples, the assay is rated an “excellent assay” for the synthetic peptide controls used and a “double assay” when used to prioritize clinical samples. Hits, defined as samples containing BChE Ser-198 adducts or no BChE present, were analyzed in a confirmatory method for identification and quantitation of the BChE adduct, if present. The ability to prioritize samples by highest exposure for confirmatory analysis is of particular importance in an exposure to cholinesterase inhibitors such as organophosphorus nerve agents, in which a large number of clinical samples may be collected. In an initial blind screen, 67 of 70 samples were accurately identified, giving an assay accuracy of 96%, and it yielded no false-negatives. The method is the first to provide a high-throughput prioritization assay for profiling adduction of Ser-198 BChE in clinical samples.