Cannabis use: consistency and validity of self-report, on-site urine testing and laboratory testing

FRANÇAIS :
Des données ont été collectées chez 248 adolescents, âgés de 12 à 18 ans, en traitement ambulatoire sur 5 sites, lors de leur entrée et au cours du traitement. La consommation déclarée à l'entrée en traitement est plus élevée que celle trouvée par les tests de dépistage sur site ou en laboratoire (respectivement 82,4%, 77%, 52,7%), mais elle est, 3 mois après, plus basse par rapport aux tests sur site et plus élevée par rapport aux tests de laboratoire (respectivement 55,5%, 70% et 47,3%). Pour deux tiers des adolescents, les tests urinaires sont positifs alors qu'ils déclarent ne avoir consommé depuis une semaine et pour un tiers, alors qu'ils déclarent ne pas avoir consommé depuis 4 semaines. Une meilleure connaissance des temps de latence de métabolisation du cannabis, aiderait à interpréter ces résultats non cohérents.
ENGLISH :
Aims. To evaluate the agreement between adolescent self-reported cannabis use, "on-site" qualitative urine screening, and quantitative laboratory testing. Design. A cross-sectional study of intake and follow-up data from 248 adolescents entering substance abuse treatment for cannabis use disorders (abuse or dependence). This is part of the multi-site cooperative agreement Cannabis Youth Treatment study. Setting. Data collected from adolescents randomly assigned to one of five out-patient treatments at four sites: Operation PAR. Inc., Florida: Chestnut Health Systems, Illinois; University of Connecticut Health Center, Connecticut; and Children's Hospital of Philadelphia, Pennsylvania. Participants. The data represent 248 unique individuals from a sample of 297 adolescents ranging in age from 12 to 18 years. Measurements. Prevalence, agreement, kappa, sensitivity, specificity, positive and negative predictive value. Findings. The self-report rates were higher at intake than either urine test (82.4%, vs. 77.0% vs. 52.7%), but both lower and higher at the 3-month follow-up (55.5% vs. 70.0% vs. 47.3%) and 6-month follow-up (60.2%, vs. 73.5% vs. 55.8%). The disagreements went in both directions and the kappa coefficients were only in the moderate range (0.4). Over two-thirds of these frequent cannabis users tested positive when they said they had not used in 1 week and one-third tested positive even though they said it had been more than 4 weeks since last use. Conclusions. The findings suggest both the advantages of multiple sources of information and the need for further work on the latency of cannabis metabolites in clinical populations. (Author' s abstract)