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Identifying new cannabis use with urine creatinine-normalized THCCOOH concentrations and time intervals between specimen collections.


A previously recommended method for detecting new cannabis use with creatinine-normalized 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (THCCOOH) urine concentrations in periodically collected specimens for treatment, workplace and judicial drug testing applications is refined by considering the time interval between urine collections. All urine specimens were collected from six less-than-daily cannabis users who smoked placebo, 1.75%, and 3.55% THC cigarettes in randomized order, each separated by one week. Ratios (n = 24,322) were calculated by dividing each creatinine-normalized THCCOOH concentration (U2) by that of a previously collected specimen (U1). Maximum, 95% limit, and median U2/U1 ratios with 15 and 6 ng THCCOOH/mL cutoff concentrations, with and without new use between specimens, were calculated for each 24-h interval after smoking up to 168 h and are included in tables. These ratios decreased with increasing interval between collections providing improved decision values for determining new cannabis use. For example, with a 15 ng THCCOOH/mL cutoff concentration and no new use between specimens, the maximum, 95% limit, and median U2/U1 ratios were 3.05, 1.59, and 0.686, respectively, when the collection interval was <or = 24 h and 0.215, 0.135, and 0.085 when it was 96-119.9 h.


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    Armed Forces Medical Examiner System, Armed Forces Institute of Pathology, Rockville, Maryland 20850, USA.



    Journal of analytical toxicology 33:4 2009 May pg 185-9


    Gas Chromatography-Mass Spectrometry
    Marijuana Abuse
    Predictive Value of Tests
    Reproducibility of Results
    Specimen Handling
    Substance Abuse Detection
    Time Factors

    Pub Type(s)

    Journal Article
    Research Support, N.I.H., Intramural
    Research Support, Non-U.S. Gov't



    PubMed ID