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Cannabis Use Surveillance by Sweat Analysis.
Gambelunghe, Cristiana PhD; Fucci, Nadia PhD; Aroni, Kyriaki PhD; Bacci, Mauro MD; Marcelli, Antonio MD; Rossi, Riccardo MD
[Article] Therapeutic Drug Monitoring. 38(5):634-639, October 2016.

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Background: Sweat testing, an alternative matrix for establishing drug abuse, offers additional benefits to the more common biological samples. The authors developed a procedure using gas chromatography-mass spectrometry to test for [DELTA]9-tetrahydrocannabinol, 11-nor-[DELTA]9-tetrahydrocannabinol-9-carboxylic acid, cannabinol (CBN), and cannabidiol (CBD) in a sweat patch. The results were compared with urine and hair sample results.

Methods: Urine, hair, and sweat samples were simultaneously collected from 12 patients who were involved, respectively, in forensic case and monitoring abuse. Selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), recovery, intraday and interday imprecision, and inaccuracy of the quantification procedure were validated. LODs in hair were 0.05 ng/mg for [DELTA]9-tetrahydrocannabinol, CBN, and CBD, and 0.005 ng/mg for 11-nor-[DELTA]9-tetrahydrocannabinol-9-carboxylic acid. The LOD for sweat was 0.30 ng/patch for all substances. The LOQ in hair was 0.1 ng/mg for [DELTA]9-tetrahydrocannabinol, CBN, and CBD, and 0.01 ng/mg for 11-nor-[DELTA]9-tetrahydrocannabinol-9-carboxylic acid. The LOQ was 0.4 ng/patch in sweat for each analyte. Cannabinoid in urine was determined by means of immunochemical screening (cutoff 11-nor-[DELTA]9-tetrahydrocannabinol-9-carboxylic acid 50 ng/mL).

Results: All subjects tested positive for 11-nor-[DELTA]9-tetrahydrocannabinol-9-carboxylic acid and [DELTA]9-tetrahydrocannabinol in urine and hair. In sweat samples, [DELTA]9-tetrahydrocannabinol was found in all patches (0.4-2.0 ng/patch); 6 cases were positive for CBN (0.4-0.5 ng/patch) and 3 for CBD (0.4-0.6 ng/patch); 11-nor-[DELTA]9-tetrahydrocannabinol-9-carboxylic acid was never detected in patches.

Conclusions: Present sweat analysis results integrated the information from hair and urine and showed that sweat analysis is a suitable, noninvasive method for monitoring compliance with rehabilitation therapy and for detecting recent cumulative use of cannabinoids.