Cut-off level is a drug testing concept that refers to that point under which a drug test is called negative and above which a drug test is called positive. For drug screening, the cut-off is determined at a point that will optimize drug detection while maintaining minimum false positive results. It is important to emphasize at this point that a negative result does not mean that a sample is drug free, only that the level of concentration of any substance that it may contain is below the defined cut-off.
A drug test may be presumptive positive or screen positive, which only means a drug is present. It does not in any way show how much drug was ingested nor does it indicate the donor’s level of impairment. All presumptive positives are followed by a confirmatory test.
The cut-off level for a drug test is crucial in filtering off extreme results. A very low and conservative drug test cut-off level may result to a lot of false positives, such as in the case of people who eat poppy seeds or become exposed to secondhand smoke. However, an extremely high cut-off level may allow drug users to test negative in the analysis. It is important for the company or organization using the drug test to strike an equilibrium drug test cut-off level. The Substance Abuse and Mental Health Services Administration has released a list of recommended cut-off levels for a number of drugs.
The figure for drug test cut-off level is usually expressed in nanograms per milliliter (ng/mL). Cut-off levels may be implemented in two types of drug tests. In screening tests, cut-off levels are set for general drug classifications such as amphetamines, barbiturates, THC and other metabolite groups. Meanwhile, confirmatory tests use gas chromatography mass spectrometry (GC/MS) to detect specific compounds and base the results on the set cut-off level for each metabolite.
Establishing the cut-off level for any particular drug test is essential in filtering off extreme results. Very low and conservative cut-off levels may return too many false positives.
For example, eating poppy seed-laden bagels prior to submitting to a drug test is believed to cause a positive result for either codeine or morphine up to 48 hours after consumption. While the poppy seeds themselves do not contain morphine, they can absorb or become coated with the opium on the pod during harvesting. About 90% of this opium is removed during processing but in many cases the poppy seeds make it all the way to store shelves still retaining a significant amount of the opium on them, but not enough that a person who consumes them should get a positive drug test for morphine, unless the cut-off level is ridiculously low.
On the other hand, inappropriately high cut-off levels result to negative results even for regular drug users. It is therefore imperative that organizations who request drug tests for their employees make sure that the testing facilities they use are following the recommended cut-off levels for various substances of abuse. The SAMHSA has a list of recommended cut-off levels typically expressed in nanograms/milliliter (ng/ml).
Cut-off levels may differ between different types of drug tests. Cut-off levels for screening tests are set for general drug categories such as marijuana, amphetamines, opiates, barbiturates, PCP and other metabolite groups. Confirmatory tests on the other hand use GC/MS (gas chromatography mass spectrometry) to detect specific compounds.
Cut-Off Levels for Drug Analytes
|Screening||Screening Cut-off Concentration||Confirmatory Test||Confirmatory Test Cut-off Concentration|
|Amphetamines1 AMP/MAMP2||500 ng/ml||Amphetamine/
|Cocaine||150 ng/ml||Benzoylecgonine||100 ng/ml|
|Marijuana||50 ng/ml||THCA3||15 ng/ml|
|MDMA4||500 ng/ml||MDMA/MDA5/MDEA6||250 ng/ml|
|Opiates Morphine/Codeine||2000 ng/ml||Morphine/Codeine||2000 ng/ml|
|Phencyclidine||25 ng/ml||Phencyclidine||25 ng/ml|
|6-Acetylmorphine||10 ng/ml||6-Acetylmorphine||10 ng/ml|
- Test kit must detect each target analyte independently at the specified cutoff.
- Methamphetamine is the target analyte for amphetamine/methamphetamine testing.
- Delta-9-tetrahydrocannabinol-9-carboxylic acid (THCA).
- Methylenedioxymethamphetamine (MDMA).
- Methylenedioxyamphetamine (MDA).
- Methylenedioxyethylamphetamine (MDEA).