title: The relationship between observed signs of impairment and THC concentration in oral fluid.
abstract: BACKGROUND
  Studies have shown that cannabis intake increases the risk of traffic accidents. Controlled experiments support these findings and have shown a positive dose-effect relationship.
  
  
  METHODS
  In this retrospective cross-sectional study of data from a roadside survey, we investigated whether a police officer's judgment regarding signs of impairment is related to the concentration of delta-9-tetrahydrocannabinol (THC) in the oral fluid (OF). We investigated 2,632 cases from a representative sample of 3,302 Spanish drivers: 253 drivers positive for THC only, 32 positive for THC and ethanol, 201 with only ethanol detected in their breath, and 2,146 drivers who tested negative for ethanol in breath and drugs in OF. Recorded data comprised breath alcohol concentrations, THC concentrations in the OF, and the 31 observed signs of impairment. Subject groups were compared using the chi-square test, and logistic regression was used to examine the risk of being categorized as exhibiting signs of impairment.
  
  
  RESULTS
  A relationship was found between the OF THC concentration and some observed signs of impairment. Eye signs were noticeable from a THC concentration >3.0 ng/ml in OF, and >25 ng/ml was related to behavior, facial expression, and speech signs. Alcohol and THC contribute to impairment independently and, when taken simultaneously, the effects are comparable to the sum of the effects when consumed separately.
  
  
  CONCLUSIONS
  The observation of signs of impairment due to cannabis occurs in an OF concentration-related manner but, as a clinical test, OF has low sensitivity and specificity in a random roadside survey.
authors.affiliation: Institute for Alcohol and Drug Studies, Faculty of Medicine, 47005-Valladolid, Spain. Electronic address: inma@lti.uva.es.
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Fierro
authors.affiliation: Directorate General for Traffic, Research Management Unit, 28071-Madrid, Spain. Electronic address: jcluque@dgt.es.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: González-Luque
authors.affiliation: Institute for Alcohol and Drug Studies, Faculty of Medicine, 47005-Valladolid, Spain. Electronic address: alvarez@med.uva.es.
authors.forename: F Javier
authors.initials: FJ
authors.lastname: Alvarez
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D055815:Young Adult; D000063:Accidents, Traffic / Q000639:trends; D000428:Alcohol Drinking / Q000009:adverse effects / Q000378:metabolism / Q000639:trends; D001334:Automobile Driving; D015415:Biomarkers / Q000737:chemistry / Q000378:metabolism; D003430:Cross-Sectional Studies; D013759:Dronabinol / Q000032:analysis / Q000378:metabolism; D012189:Retrospective Studies; D012307:Risk Factors; D012463:Saliva / Q000737:chemistry / Q000378:metabolism
chemical_list: D015415:Biomarkers; D013759:Dronabinol
keywords: Cannabinoids; automobile driver examination; diagnostic test; psychomotor impairment; traffic accidents