Examination of Firearms Review: 2007 to 2010 - Interpol

measured by LC-MS, declined from 348 to 3.9 ng/mL over a surprisingly long
period of 12 weeks (84 days), but were supported by her THCCOOH excretion
profile, indicating that special caution is needed in interpreting urine test results
from heavy, chronic cannabis users [118]. To test the validity of THC and
11-hydroxy-THC (11-OH-THC) in urine as indicators of recent cannabis use,
urinary cannabinoid excretion in 33 chronic cannabis smokers, who resided on
a secure research unit under 24 h continuous medical surveillance, were
monitored. Extended urinary excretion of THC and 11-OH-THC was observed
for at least 24 days, negating their effectiveness as biomarkers of recent
cannabis exposure, and substantiating long terminal elimination times for
urinary cannabinoids following chronic cannabis smoking [119]. The time
course of THCCOOH elimination in urine was characterized in 60 cannabis
users during 24 h monitored abstinence for up to 30 days, with urine samples
taken for GC-MS analysis. Data were divided into three groups, 0-50, 51-150,
and > 150 ng/mg, and results from this study showed that the number of days
until first negative and last positive urine specimens for the three groups were
0.6 and 4.3, 3.2 and 9.7, and 4.7 and 15.4 days, respectively [120].
In a retrospective study of a military testing program that had been conducted
over a three-year period, it was found that 50% of all positive marijuana and
cocaine urine metabolite were below median values of 65 and 968 ng/mL,
respectively. A median drug concentration combined with the percentile or
frequency that a particular urine drug concentration occurs, may provide useful
information for evaluation [121]. 22 urine specimens reported by the same
group for the presence of high concentrations of amphetamine only (28,028 to
241,142 ng/mL) were subjected to further analysis for the presence of
methamphetamine (MA) [ 122 ]. It has been suggested that a urine
concentration ratio of MA to amphetamine less than 0.5%, with similar isomeric
distribution of d-(S) and l-(R) amphetamine and MA, respectively, may not
necessarily indicate the use of both amphetamine and MA.
A study reported that increased storage temperatures were associated with
increased urine pH, which might be due to degradation of nitrogenous urine
[123]. The pH values of specimens stored at -20 o C are relatively stable,
whereas pH results > 9 are achieved when samples are stored at room
temperature or higher. Statistical data of consecutive urine-creatinine
concentrations were evaluated as a laboratory marker of urine dilution [124].
The 2.5-97.5% percentile ranges for women were: 129-2690 mg/L, while for
men were 204-3520 mg/L. Using cut-offs greater than the gender-specific
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