Journal of Analytical Toxicology 2012;36:291 doi:10.1093/jat/bks034
Letter to the Editor
Is THC-COOH a Useful Determinant for Passive Inhalation in Oral Fluid THC Testing?
To the Editor: Many studies have demonstrated that passive exposure to marijuana smoke can lead to detectable concentrations of tetrahydrocannabinol (THC) in oral fluid (OF) (1 –3). It is reasonable to assume that subjects breathing air heavily laden with THC will absorb some of the drug. An important related issue is how long concentrations will remain detectable. The magnitude of the exposure depends greatly on many variables, including the duration of exposure, the potency of the marijuana being smoked, and the concentration of smoke in the enclosed space (i.e., room size, number of smokers and number of passive inhalers). Peak concentrations in OF have generally been observed at the end of exposure followed by a rapid decline typically within one hour (1, 2). Recently, Moore et al. (3) found that although THC was present in the OF sampled from the passively exposed subjects, no THC carboxy acid metabolite (THC-COOH) was detected at a cutoff of 2 pg/mL. The authors concluded that THC-COOH is likely to be a valid marker for active marijuana use, and recommended that “in order to avoid false positive oral fluid results assigned to marijuana use, by analyzing for only THC, the metabolite THC-COOH should also be monitored.” In our view, two key issues for workplace drug testing programs are raised by this research. First is the question of the validity of THC-COOH as a unique marker of cannabis use. We believe that for a marker to be useable, it must be scientifically validated that the marker occurs only in the “true” condition (characterized by such variables as dose response, time course of appearance and disappearance, and potential interferences (false positives) and does not occur in the “false” condition (no active use). It is well known that THC-COOH reaches peak concentrations in plasma at 0.5 to 4 hours and in urine at 8 to 14 hours, thus indicating a delay or lag time necessary for THC to be metabolized to THC-COOH in the liver, released into the blood and excreted in body fluids. Therefore, THC-COOH may have been present in the passively exposed subjects’ OF at times not sampled in previous studies. Second, for drug testing program policy makers, a major question is how likely it is that an individual would get sufficient passive exposure to test positive at some later time. At present, it remains unclear how long detectable levels of THC persist after the exposure ends. The answer to this question needs to be explored scientifically by evaluating dose-response,
time-course, and other potential interferences to elucidate the “wash-out” effect. The Niedbala et al. studies (1, 2) found that one hour after exposure, the passive inhalers no longer tested positive for THC. In the Moore et al. study (3), post-exposure specimens were only collected between 12 and 22 hours post exposure and 8 of 10 subjects had non-detectable THC concentrations, and the other two subjects had ,1.1 ng/mL THC, which is well below most workplace OF cutoffs. Based on the data available, we believe the conclusion that THC-COOH is a valid marker for marijuana use may be premature. Understanding and documenting the science of OF testing, especially when used as a matrix for workplace and law enforcement, testing is critically important, especially for the detection of marijuana use. The use of OF testing is increasing, and marijuana is the most prevalent illegally used substance globally. We encourage further research to clarify these issues and we applaud the research that has been so far accomplished.
References 1. Niedbala, R.S., Kardos, K.W., Fritch, D.F., Kardos, S., Fries, T., Waga, J. et al. (2001) Detection of marijuana use by oral fluid and urine analysis following single-dose administration of smoked and oral marijuana. Journal of Analytical Toxicology, 25, 289–303. 2. Niedbala, R.S., Kardos, K.W., Fritch, E.F., Kunsman, K.P., Blum, K.A., Newland, G.A. et al. (2005) Passive cannabis smoke exposure and oral fluid testing. II. Two studies of extreme cannabis smoke exposure in a motor vehicle. Journal of Analytical Toxicology, 29, 607– 615. 3. Moore, C., Coulter, C., Uges, D., Tuyay, J., van der Linde, S., Van, L.A. et al. (2011) Cannabinoids in oral fluid following passive exposure to marijuana smoke. Forensic Science International, 212, 227–230.
J. Michael Walsh1*, Edward J. Cone2, Dennis J. Crouch3 and Yale H. Caplan4 1 The Walsh Group, Bethany Beach, DE 2 Johns Hopkins School of Medicine, Baltimore, MD 3 Utah Expert-Toxicology Services, Salt Lake City, UT 4 University of Maryland, School of Pharmacy, Department of Pharmaceutical Sciences, Baltimore, MD *Author to whom correspondence should be addressed. Email:
[email protected].
# The Author [2012]. Published by Oxford University Press. All rights reserved. For Permissions, please email:
[email protected]
