Quote Originally Posted by Burnt Toast
An assay will be performed first and if the sample fails that, THEN the GC/MS will be performed on the drug(s) that failed the assay. It would be way too costly to use the GC/MS as the primary methodology.


Dont let the differing cutoff levels freak you out. Although their cutoffs numerically differ, a 50 ng assay is functionally equivalent to the 15 ng GC/MS. Their cutoffs differ because the assay recognizes all 31 metabolite concentrations combined, while the GC/MS recognizes only 1 metabolite concentration.

THC enters the body in its ingested form and exits the body as 31 different metabolite concentrations. The most prevalent metabolite concentration is the 11-nor-delta-9-carboxy-THC (aka "THC-COOH") concentration.
In order to test negative on the assay, the combination of all 31 metabolite concentrations must register below 50 ng.
In order to test negative on the GC/MS, only that one metabolite concentration (THC-COOH) must register below 15 ng.
thanks a lot for the info.
do you know if water is/can be considered a sample adulteration or substitution? or if the lab can distinguish between a person drinking excess water or adding water to their sample? i'm trying to get an idea of what result i could expect back after pouring some water into a lab sample to dilute it.
sic1231 Reviewed by sic1231 on . MedTox Lab Test. Help? I was sent to the hospital by my employer for a drug test yesterday. I'm worried they're going to skip the initial immunoassay test, since it appears the tests ordered are GC/MS confirmation tests with reduced cutoff levels. One of the test codes is 149. The description of this test code on the test catalog portion of the MedTox website (MEDTOX : Test Catalog) reads: "Quantitative result is marijuana metabolite measured as 11-nor-delta-9-carboxy-THC (carboxy-THC) by gas chromatography with Rating: 5