Drug and Alcohol Testing Q&A - 2004

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"Impairment" inferred from THC conc. in urine

From: Quentin Fannin, M.D., MRO-C.
Date: 10 Mar 2004
Time: 08:25:12 -0800
Remote Name: 199.91.33.254

Comments

I was asked to comment by an employer and employer's attorney regarding the impairment of a donor from marijuana whose post accident drug screen was positive for carboxy-THC at 597 ng/ml.  I am aware that there has been no level associated with impairment of an individual, but most of the sources say "...there is some level at which impairment exists...".  I have reviewed several papers available to me; most measure blood levels.  Is there a numerical relationship between urine levels of THC and serum levels?  Is there an obvious or intuitive level at which impairment might be considered to exist?  At 100ng/ml in urine?...at 500ng/ml...at 1000ng/ml?  Thanks for your help on this and over the years.