In workplace drug testing, the industry standard process involves two-tiered testing – an initial screen on one portion of the specimen, followed by a confirmatory test on a second portion of the original specimen. The initial test is designed to separate negative specimens from further consideration. The confirmatory test uses definitive methods, such as chromatography-mass spectrometry (e.g., GC-MS, LC-MS/MS), that specifically identify and quantify the drug/metabolite in the specimen. Drug testing detects the presence of drugs and drug metabolites using cutoff levels to determine whether a specimen tests positive or negative for the use of a specific drug.
Cutoff levels are expressed in nanograms (ng) per milliliter (mL) for urine and oral fluid testing or picograms (pg) per milligram (mg) for hair testing. It is important to select a specimen type and cutoff level based on the desired window of detection and any regulatory requirements. Only when a drug or drug metabolite is identified at a concentration equal to or above the administrative cutoff is a specimen reported by the laboratory as positive. Consequently, a negative drug test does not necessarily mean that no drug is present. While that may be the case, other possible interpretations are that a drug was present below the cutoff or the testing panel did not include the drug the individual was using.
Cutoff levels for federally-regulated drug testing programs are established based on mandatory guidelines set by U.S. Department of Health and Human Services (HHS). Additionally, the U.S. Department of Transportation’s (DOT) rule 49 CFR Part 40 harmonizes with HHS and describes the required procedures for conducting drug and alcohol testing for the federally-regulated transportation industry. Many non-regulated employers mirror the cutoff levels established by the government while others customize their drug testing panels to be more sensitive to certain drugs based upon their program needs and unique workforce.
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