Validation of an enzyme immunoassay for detection and semiquantification of cannabinoids in oral fluid.
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.
Schwope
David M
DM
Chemistry and Drug Metabolism, National Institute on Drug Abuse, NIH, Baltimore, MD 21224, USA.
Milman
Garry
G
Huestis
Marilyn A
MA
D002188:Cannabis / Q000737:chemistry; D013759:Dronabinol / Q000031:analogs & derivatives* / Q000032:analysis / Q000276:immunology; D006801:Humans; D013287:Illicit Drugs / Q000032:analysis*; D007124:Immunoenzyme Techniques / Q000379:methods*; D057230:Limit of Detection; D008297:Male; D012463:Saliva / Q000737:chemistry*; D015813:Substance Abuse Detection / Q000379:methods*
D013287:Illicit Drugs; D013759:Dronabinol; C025351:delta(9)-tetrahydrocannabinolic acid