A cutoff level is the concentration of a drug or its metabolite, measured in nanograms per milliliter (ng/mL), that a lab uses to call a sample positive. For federally regulated urine tests, the screen cutoff is 50 ng/mL of THC-COOH, the main cannabis metabolite. The confirmation cutoff is 15 ng/mL. Private employers set their own numbers and often go lower.
Federal urine cutoffs
The Department of Health and Human Services sets cutoffs for federal workplace testing. The Department of Transportation adopts those numbers for truck drivers, pilots, and other safety-sensitive jobs.
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- Immunoassay screen: 50 ng/mL THC-COOH
- GC-MS or LC-MS/MS confirmation: 15 ng/mL THC-COOH
HHS raised the urine screen cutoff from 100 ng/mL to 50 ng/mL in 1998. It has not changed since.
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Cutoffs by specimen
- Urine: 50 ng/mL screen, 15 ng/mL confirmation (federal)
- Oral fluid: 4 ng/mL screen, 2 ng/mL confirmation (HHS guidelines published in 2023)
- Hair: 0.1 ng/mg, equal to 1 pg/mg, at most labs
- Blood: no federal cutoff. Each lab publishes its own, and some report at 1 ng/mL or less.
Private and instant panels
Non-DOT employers buy panels with cutoffs of 50, 20, 15, 10, or 5 ng/mL. A lower cutoff catches less drug but returns more positives from passive exposure and lab error. Instant urine cups sold for home and workplace use almost all use a 50 ng/mL screen. They give a result in minutes and no confirmation step unless the sample goes to a lab.
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Detection windows
The cutoff sets the floor. The window depends on dose, body fat, and use pattern.
- Urine after one use: 1 to 3 days
- Urine after heavy daily use: up to 30 days
- Oral fluid: hours to 2 days
- Hair: about 90 days, matching the growth of the sample
Dilution and validity testing
A sample below the cutoff is not always a clean sample. Labs flag urine as dilute when creatinine is under 20 mg/dL and specific gravity is under 1.0030. Federal rules require a second collection under direct observation when a sample is dilute.
Convenience and point-of-care testing
The move to instant tests changed which cutoffs people see. An oral fluid swab at a roadside or a front desk gives a result in minutes at a 4 ng/mL screen, while a lab urine test reports against 50 ng/mL. The two numbers are not the same test and do not compare. Convenience sets the format. The cutoff still decides the result.