An initial Immunoassay screen (at a 50 ng cutoff limit) is done first. It would be way too costly to use the 15 ng GC/MS as the primary analysis.

Even on the off-chance that the GC/MS is used first, dont let it worry you. A 50 ng Immunoassay is functionally equivalent to the 15 ng GC/MS. For more info on this, read post #22 in this thread: http://boards.cannabis.com/drug-test...aking-out.html