All positive initial screens should be confirmed by GC/MS (Gas Chromatagraph/Mass Spectrometry) at a DHHS/SAMHSA certified laboratory. This is due to the fact that any laboratory or on-site/instant drug screen, no matter how accurate, is not 100% accurate in identifying drugs of abuse in urine. The initial screens react to multiple drug metabolites, and can under certain non-ideal situations, produce a positive result when the target drug is not present or is present at a level below the GC/MS confirmation cut-off level. GC/MS confirmation is a more specific test that looks for and if present quantifies the target metabolite. It is the GC/MS confirmation through a certified laboratory that will stand up in the court of law if the drug test result is challenged by the donor.
Sending the specimen to a lab as a “Blind screen” where the specimen will be screened by the laboratory, and if found positive by the lab screen, will be confirmed by GC/MS at the lab. The error with this method is that the lab screen may produce a negative result on a specimen that is near the screen cut-off and that would confirm by GC/MS. However, the specimen will never be sent to GC/MS for confirmation if the labscreen calls the specimen “negative”. Therefore, any error or inaccuracy in the lab screen will result in a “true positive” specimen being ruled “negative”