Once the sample goes to a lab, an Immunoassay screen is conducted first, with a 50 ng/ml cutoff limit for THC. If the sample is positive, then the sample will undergo a confirmation GC/MS with a 15 ng cutoff level.

Dont let the differing cutoff levels between the two types of tests worry you. Even though their cutoffs numerically differ, a 50 ng assay is functionally equivalent to the 15 ng GC/MS. Their cutoffs numerically differ because the assay recognizes all 31 metabolite concentrations combined, while the GC/MS recognizes only one metablite concentration (THC-COOH). For more info on this, read my posts in this thread:

http://boards.cannabis.com/drug-test...d-testing.html