The standard THC test is a one step rapid, qualitative immunoassay for the detection of tetrahydrocannabinol compounds (9-carboxy-THC) in urine. The cutoff concentration recommended by the Substance Abuse and Mental Health Services Administration (SAMHSA/NIDA) for a positive result in an immunoassay test is 50 ng/ml. The cutoff for GC-MS is generally 15 ng/ml.

The standard THC test cutoff for GC-MS is generally 15 ng/ml.

It is highly unlikely that court ordered testing sites are going to use 20 ng/ml cut off. Further, court ordered testing usually requires that you either go to a specific site or to a specific lab company who has more than one site.

The initial screening cutoff level is 50 ng/ml. The GC/MS cutoff level is 15 ng/ml. The elimination half-life of marijuana ranges from 14-38 hours. At the initial cutoff of 50 ng/ml, the daily user will remain positive for perhaps 7 to 30 days after cessation. At the confirmation level of 15 ng/ml, the frequent user will be positive for perhaps as long as 15 weeks. Marijuana metabolites' storage and slow release from lipid tissues is the reason for this long detection period.

That is why the court is most likely going to use a site that uses the 15ng/ml level.

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