Evaluation of a homogenous enzyme immunoassay for the detection of synthetic cannabinoids in urine

Abstract

Introduction: The recent emergence and widespread availability of many new synthetic cannabinoids support the need for an accurate and high-throughput urine screen for these new designer drugs. We evaluated performance of the immunalysis homogeneous enzyme immunoassay (HEIA) to sensitively, selectively, and rapidly identify urinary synthetic cannabinoids.

Methods: 2443 authentic urine samples were analyzed with the HEIA that targets JWH-018 N-pentanoic acid, and a validated LC-MS/MS method for 29 synthetic cannabinoids and metabolites. Semi-quantitative HEIA results were obtained, permitting performance evaluation at and around three cutoffs (5, 10 and 20 μg/L), and diagnostic sensitivity, specificity and efficiency determination. Performance challenges at ±25 and ±50% of each cutoff level, cross-reactivity and interferences also were evaluated.

Results: Sensitivity, specificity, and efficiency of the immunalysis HEIA K2 Spice kit with the manufacturer's recommended 10 μg/L cutoff were 75.6%, 99.6% and 96.8%, respectively, as compared to the reference LC-MS/MS method with limits of detection of 0.1-10 μg/L. Performance at 5 μg/L was 92.2%, 98.1% and 97.4%, and for the 20 μg/L cutoff were 62.9%, 99.7% and 95.4%. Semi-quantitative results for in-house prepared standards were obtained from 2.5-30 μg/L, and documented acceptable linearity from 5-25 μg/L, with inter-day imprecision <30% (n = 17). Thirteen of 74 synthetic cannabinoids evaluated were classified as highly cross-reactive (≥50% at 10 μg/L); 4 showed moderate cross-reactivity (10-50% at 10 μg/L), 30 low cross-reactivity (<10% at 500 μg/L), and 27 <1% cross-reactivity at 500 μg/L. There was no interference from 102 investigated compounds. Only a mixture containing 1000 μg/L each of buprenorphine/norbuprenorphine produced a positive result above our proposed cutoff (5 μg/L) but below the manufacturer's recommended cutoff concentration (10 μg/L).

Conclusion: The Immunalysis HEIA K2 Spice kit required no sample preparation, had a high-throughput, and acceptable sensitivity, specificity and efficiency, offering a viable method for screening synthetic cannabinoids in urine that cross-react with JWH-018 N-pentanoic acid antibodies.

Keywords: HEIA; Immunoassay; Synthetic cannabinoids.

Fig. 1

General structures of synthetic cannabinoids (A–M).

Fig. 2

Linearity evaluation with the quantile-quantile plot for fortified performance challenge samples (5-30 μg/L) analyzed in 17 batches. Duplicate values were averaged in each run and mean concentrations were plotted vs. known concentrations. Straight line corresponds to 100% agreement with the predicted concentration. Dashed lines are ±30% of target concentrations.