> -----Original Message-----
> My understanding is that cannabis can remain detectable in
> urine ( >50 ug/l) for
> around 4 weeks after the last drug usage.Furthermore at the
> approach to no drug detection the urines can vary from
> positive to negative depending on dilution and other
> factors.This makes establishing whether the client is
> continuing to abuse cannabis quite difficult.How do
> list-users out there handle this situation?
The evidence for prolonged excretion of cannabinoids is credible, but
largely anecdotal. Conventional wisdom holds that heavy use of marijuana
over some time is required to produce the type of scenario you describe.
Cannibinoids are typically cleared within a few days following occasional
use.
With regard to your question about the reliability of urine drug testing
results, you correctly observe that results are influenced by, among other
things, the hydration status of the subject. Drug testing labs in the U.S.
ordinarily apply several "specimen integrity" checks, including tests for
excessive dilution (specific gravity and/or creatinine). But even given
these precautions, it is an unaviodable fact that (confirmed) positive drug
testing results are far more meaningful than negative results.
Screening reagents that detect cannibinoids at a threshold of 20 ng/mL are
available, and their use improves the clinical sensitivity somewhat.
Roger
Roger L. Bertholf, Ph.D.
Associate Professor of Pathology
Director of Clinical Chemistry & Toxicology
University of Florida Health Science Center/Jacksonville
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