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malaprop · May 28, 2011, 06:08 PM

I have to have a drug test next week at Quest Diagnostics. The dipstick test I had done came up positive for marijuana. It is called Marijuana, GC/MS, Urine. I googled it and found it is also called Marijuana Metabolites, GC/MS, Urine depending on which Quest facility is doing the test. I also found that a couple of other people have posted online asking what this test looks for. I could not find a clear answer. Does anyone know if this looks for several marijuana metabolites or 11-COOH-THC?

P.S. I tried contacting Quest, but they will provide absolutely no info on what the test measures/

DrBill100 · May 28, 2011, 07:24 PM

Originally Posted by malaprop

I have to have a drug test next week at Quest Diagnostics. The dipstick test I had done came up positive for marijuana. It is called Marijuana, GC/MS, Urine. I googled it and found it is also called Marijuana Metabolites, GC/MS, Urine depending on which Quest facility is doing the test. I also found that a couple of other people have posted online asking what this test looks for. I could not find a clear answer. Does anyone know if this looks for several marijuana metabolites or 11-COOH-THC?

P.S. I tried contacting Quest, but they will provide absolutely no info on what the test measures/

Practically, it's both but the difference is inconsequential. COOH (11-nor-9-carboxy-delta9-THC) is the target metabolite but there can be cross-reactivity with some other cannabinoids (this is at level of immunoassay, IA).

Despite the fact that GC/MS is included in the test nomenclature, the instrument isn't standardly used unless there is a presumptive positive by IA. GC/MS can always be specifically ordered but generally isn't. It is used only for confirmation.

COOH is the metabolite of significance. I too have seen numerous questions, such as yours, questioning specifics on other metabolites. The accepted standard is COOH and I fail to understand why it's important if additional metabolites were detected. What have I missed?

Quest, and other major laboratories offer a wide range of tests geared to the requirements of the requesting party. You will not get specifics on the test from them, or any other laboratory. That has to do with protecting their procedures from competitors.

malaprop · May 31, 2011, 07:00 PM

I took the test today and was told if my level exceeded 50 I would fail. I thought it would be 15 based on what I have read. It is a GC/MS, but I think the test must be measuring more than COOH.

DrBill100 · May 31, 2011, 07:56 PM

Originally Posted by malaprop

I took the test today and was told if my level exceeded 50 I would fail. I thought it would be 15 based on what I have read. It is a GC/MS, but I think the test must be measuring more than COOH.

The confirmation level is 15 using the GC/MS. Have never heard of a 50 confirmatory. Both numbers 50 (for screening) and 15 (for confirmation) apply to THC-COOH.

GC/MS is capable of identifying and quantifying even minor cannabinoids, so they could test for any number. But that would be very unusual, not to mention expensive. The type of test requested is the determining factor. But at the cutoffs you mention the only possibility is COOH.