Validation of the only commercially available immunoassay for synthetic cathinones in urine: Randox Drugs of Abuse V Biochip Array Technology

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Abstract
Deterrence of synthetic cathinone abuse is hampered by the lack of a high‐throughput immunoassay screen. The Randox Drugs of Abuse V (DOA‐V) Biochip Array Technology contains two synthetic cathinone antibodies: Bath Salt I (BSI) targets mephedrone/methcathinone and Bath Salt II (BSII) targets 3’,4’‐methylenedioxypyrovalerone (MDPV)/3’,4’‐methylenedioxy‐α‐pyrrolidinobutiophenone (MDPBP). We evaluated DOA‐V synthetic cathinones performance and conducted a full validation on the original assay with calibrators reconstituted in water, and the new assay with calibrators prepared in lyophilized urine; both utilized the same antibodies and were run on the fully automated Evidence® Analyzer. We screened 20 017 authentic military urine specimens and confirmed positives by liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) for 28 synthetic cathinones. Limits of detection (LOD) for the original and new assays were 0.35 and 0.18 (BSI), and 8.5 and 9.2 µg/L (BSII), respectively. Linearity was acceptable (R2 > 0.98); however, a large negative bias was observed with in‐house prepared calibrators. Intra‐assay imprecision was <20% BSI‐II, while inter‐assay imprecision was 18‐42% BSI and <22% BSII. Precision was acceptable for Randox controls. Cross‐reactivities of many additional synthetic cathinones were determined. Authentic drug‐free negative urine pH <4 produced false positive results for BSI (6.3 µg/L) and BSII (473 µg/L). Oxidizing agents reduced BSI and increased BSII results. Sensitivity, specificity, and efficiency of 100%, 52.1%, and 53.0% were obtained at manufacturer's proposed cut‐offs (BSI 5 µg/L, BSII 30 µg/L). Performance improved if cut‐off concentrations increased (BSI 7.5 µg/L, BSII 40 µg/L); however, there were limited confirmed positive specimens. Currently, this is the first and only fully validated immunoassay for preliminary detection of synthetic cathinones in urine. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
Funding Information
  • National Institute on Drug Abuse
  • Department of Defense Counter Narcotics Program

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