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, 56 (6), 1007-14

Validation of an Enzyme Immunoassay for Detection and Semiquantification of Cannabinoids in Oral Fluid


Validation of an Enzyme Immunoassay for Detection and Semiquantification of Cannabinoids in Oral Fluid

David M Schwope et al. Clin Chem.


Background: Oral fluid (OF) is gaining prominence as an alternative matrix for monitoring drugs of abuse in the workplace, criminal justice, and driving under the influence of drugs programs. It is important to characterize assay performance and limitations of screening techniques for Delta(9)-tetrahydrocannabinol (THC) in OF.

Methods: We collected OF specimens by use of the Quantisal OF collection device from 13 daily cannabis users after controlled oral cannabinoid administration. All specimens were tested with the Immunalysis Sweat/OF THC Direct ELISA and confirmed by 2-dimensional GC-MS.

Results: The limit of detection was <1 microg/L THC equivalent, and the assay demonstrated linearity from 1 to 50 microg/L, with semiquantification to 200 microg/L. Intraplate imprecision (n = 7) ranged from 2.9% to 7.7% CV, and interplate imprecision (n = 20) was 3.0%-9.1%. Cross-reactivities at 4 microg/L were as follows: 11-hydroxy-THC, 198%; Delta(8)-tetrahydrocannabinol (Delta(8)-THC), 128%; 11-nor-9-carboxy-THC (THCCOOH), 121%; THC (target), 98%; cannabinol, 87%; THCCOOH-glucuronide, 11%; THC-glucuronide, 10%; and cannabidiol, 2.4%. Of 499 tested OF specimens, 52 confirmed positive (THC 2.0-290 microg/L), with 100% diagnostic sensitivity at the proposed Substance Abuse and Mental Health Services Administration screening cutoff of 4 microg/L cannabinoids and GC-MS cutoff of 2 microg/L THC. Forty-seven specimens screened positive but were not confirmed by 2D-GC-MS, yielding 89.5% diagnostic specificity and 90.6% diagnostic efficiency. Thirty-one of 47 unconfirmed immunoassay positive specimens were from 1 individual and contained >400 ng/L THCCOOH, potentially contributing to cross-reactivity.

Conclusions: The Immunalysis Sweat/OF THC Direct ELISA is an effective screening procedure for detecting cannabinoids in OF.

Conflict of interest statement

Authors’ Disclosures of Potential Conflicts of Interest: Upon manuscript submission, all authors completed the Disclosures of Potential Conflict of Interest form. Potential conflicts of interest:

Employment or Leadership: None declared.

Consultant or Advisory Role: None declared.

Stock Ownership: None declared.

Honoraria: None declared.

Other Remuneration: D.M. Schwope, Immunalysis Corporation. (It sponsored an open competition for a travel grant; this author won the competition and has received travel funding from Immunalysis Corporation to present this research at a scientific meeting.)

Expert Testimony: None declared.


Fig. 1
Fig. 1. Immunalysis Sweat/Oral Fluid Δ9-THC Direct ELISA linearity
Linearity determined with in-house calibrators (●) prepared by fortifying centrifuged, buffered OF with THC. Evaluation from 1–50 µg/L THC yielded a logarithmic regression line in good accordance with manufacturer-provided calibrators and controls (+). Logit values (L) were calculated as L = ln[(B/B0)/(1 – (B/B0))].
Fig. 2
Fig. 2. Mean (n = 3) (range) cannabinoid cross-reactivity in fortified authentic OF in the Immunalysis Sweat/Oral Fluid Δ9-THC Direct ELISA
Dashed line represents 4 µg/L THC (target) cross-reactivity (98%). Individual cross-reactivity samples quantifying less than negative control were included in means as having 0% cross-reactivity. +, sample qualitatively positive.

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