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

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-alpha-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 (R) 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 mu g/L (BSII), respectively. Linearity was acceptable (R-2 > 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 mu g/L) and BSII (473 mu g/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 mu g/L, BSII 30 mu g/L). Performance improved if cut-off concentrations increased (BSI 7.5 mu g/L, BSII 40 mu g/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.