What is the cutoff level?
One of the key concepts within drug testing is the application of a cutoff level. This is the point which seperates a test result as being either positive or negative.
For drug tests, a cutoff is chosen that will optimise drug detection but minimise the number of false positive results. It is important to note that a negative sample doesn’t mean that it is drug free; it might contain a drug at a concentration that is lower than the defined cut-off.
If a drug test is reported as screen positive or presumptive positive, this merely shows a response, which is usually because a drug is present. It cannot show how much drug was taken or be correlated to any degree of impairment. As this is a screening tool, all presumptive positives require a confirmation test.
| Drug | Cut-Off Level | Minimum Detection Time * | Maximum Detection Time * |
|---|---|---|---|
| Marijuana (THC) | 50 ng/ml | 2 hours | Up to 5+ days |
| Cocaine (COC) | 300 ng/ml | 1 – 4 hours | 2 – 4 days |
| Amphetamine (AMP) | 1000 ng/ml | 2 – 7 hours | 2 – 4 days |
| Methamphetamine (MET) | 1000 ng/ml | 2 – 7 hours | 2 – 4 days |
| Morphine (MOP) | 300 ng/ml | 2 hours | 2 – 3 days |
| Morphine (2000) Opiates | 2000 ng/ml | 2 hours | 2 – 3 days |
| Methylenedioxymethamphetamie (MDMA) | 500 ng/ml | 2 – 4 hours | 2 – 4 days |
| Barbiturate (BAR) | 300 ng/ml | 2 – 4 hours | 1 – 3 weeks |
| Benzodiazepines (BZO) | 300 ng/ml | 2 – 7 hours | 1 – 4 days |
| Methadone (MTD) | 300 ng/ml | 3 – 8 hours | 1 – 3 days |
| Oxycodone (OXY) | 100 ng/ml | 1 – 3 hours | 1 – 2 days |
| Phencyclidine (PCP) | 25 ng/ml | 4 – 6 hours | 7 – 14 days |
| Tri-Cyclic Antidepressants (TCA) | 1000 ng/ml | 8 – 12 hours | 2 – 7 days |
| Buprenorphine (BUP) | 10 ng/ml | 4 hours | 1 – 3 days |
This assay provides only a preliminary test result. A more specific alternative chemical method must be used in order to obtain a confirmed analytical result. Gas chromatography/mass spectrometry (GC/MS) is the preferred confirmatory method. Clinical consideration and professional judgment should be applied to any drug of abuse test result, particularly when preliminary results are positive.
