What are drug cut-off levels and why do we need them?

What are drug cut-off levels and why are they needed?

  • What are the Cut-Off levels?
  • Should I use a laboratory?
  • What are the detection times?

Why do we need a cut-off level?

When testing for drugs, there needs to be a control in place to establish the point when negative becomes positive. This control or level is set by the manufacturer from recommendations set by (NIDA) a department of the US government. It is important to note that a negative sample doesn’t mean that it is drug-free; it might contain a drug that is at a concentration lower than the defined cut-off level.

What are the Cut-Off levels?

Drugs of Abuse Screening Tests are one-step lateral flow immunoassay intended for the detection of drugs in urine. Drug Screening Tests are assays for use in the qualitative detection of drugs of abuse overseen by the Substance Abuse Mental Health Services Administration (SAMHSA).

A cut-off level is a point at which a test is either a presumed positive or negative. A positive result is when a drug detected is above that set level for that drug. For example, if cocaine was detected, the level for detection will be above 300 ng/ml. The recommended levels vary for each drug and can be seen in more detail in the tables below. Urine and Oral/Saliva screening provide only preliminary results. If a Presumed positive is detected then an alternative method must be used in order to obtain a confirmed analytical result.

Results from a assay are displayed in panels on the face of the device. In the images below, each assay shows colored lines or bars, one in the (C) area and one in the (T) area. A presumed positive is when only one colored line is visible (C) with no apparent line in the (T) area.

Fig 1.

Fig 2.

Fig 3.

The images above tell us the result of a drug screen under different scenarios. In Fig 1., the image shows the results are negative as all lines/bars are visible. In Fig 2., this is a presumed positive when no (T) line or bar is visible. In this example, it applies to Cocaine and Opiates; The metabolite of Cocaine has been detected at a level higher than 300 ng/ mL and the metabolite for Opiates at a level over 2000 ng/mL. Anything higher than these levels is positive. Have the sample be confirmed utilizing a technique called Gas Chromatography-Mass Spectrometry at a SAMHSA approved lab. Fig 3. is the result of an invalid test, generally due to insufficient sample volume.

Should I use a laboratory if the drug cut-off levels show the result is positive?

A laboratory should always be used to confirm a presumed positive urine sample. Whenever you get a presumed positive, it is impossible to know how much is in their system and if the rapid test worked correctly. A laboratory will test your sample and confirm your suspicions with a method called Gas Chromatography-Mass Spectrometry (GC-MS); This is the preferred method for testing and will quantitate the amount found reported in pg/mL. Always use a SAMHSA certified laboratory for testing.

GC/MS confirmation is unequivocal when looking for drugs and quantifies the target metabolite with a number. If a donor challenges the test result, a GC/MS confirmation from a certified laboratory will stand up in the court of law.

All FDA cleared drug screening test results always adhere to strict cut-off levels, as can be seen in the charts below.
Source: National Institute on Drug Abuse (NIDA).

Urine Cut-Off Levels

Drug Name Code Detection Time Cut-Off level
Amphetamines AMP 2-4 Days 1000 ng/mL
Barbiturates BAR 4-7 Days 300 ng/mL
Benzodiazepines BZO 3-7 Days 300 ng/mL
Buprenorphine BUP 1-3 Days 10 ng/mL
Cocaine COC 2-4 Days 300 ng/mL
Ecstasy MDMA 1-3 Days 500 ng/mL
EtG Alcohol EtG Up to 80 Hours 300 ng/mL
Fentanyl FEN 1-3 Days 200 ng/mL
Marijuana THC 2-30 Days 50 ng/mL
Methadone MTD 3-5 Days 300 ng/mL
Methamphetamine mAMP 3-5 Days 1000 ng/mL
Morphine MOR 2-4 Days 300 ng/mL
Opiates OPI 2-4 Days 2000 ng/mL
Oxycodone OXY 2-4 Days 100 ng/mL
Phencyclidine PCP 7-14 Days 25 ng/mL
Propoxyphene PPX 1-2 Days 300 ng/mL
Synthetic Marijuana K2/Spice 2-10 Days 50 ng/mL
Tricyclic Antidepressants TCA 7-10 Days 1000 ng/mL

Saliva Cut-Off Levels

Drug Name Code Detection Time Cut-Off Level
Alcohol ALC 6-12 Hours >0.02% B.A.C.
Amphetamines AMP 1-3 Days 50 ng/mL
Barbiturates BAR 3-5 Days 300 ng/ml
Benzodiazepines BZO 1-3 Days 50 ng/ml
Buprenorphine BUP 1-3 Days 5 ng/mL
Cocaine COC 1-3 Days 20 ng/mL
Ecstasy MDMA 1-3 Days 50 ng/mL
Fentanyl FEN 1-3 Days 10 ng/mL
Marijuana THC 6-12 Hours 25 ng/mL
Methadone MTD 5-7 Days 75 ng/ml
Methamphetamine mAMP 1-3 Days 50 ng/mL
Opiates OPI 2-5 Days 40 ng/mL
Oxycodone OXY 2-5 Days 50 ng/mL
Phencyclidine PCP 1-3 Days 10 ng/mL
Propoxyphene PPX 1-3 Days 50 ng/mL
Tramadol TRA 12-24 Hours 50 ng/mL
Tricyclic Antidepressants TCA 1-2 Days 50 ng/mL

What are the detection times?

Detection times are estimates and apply only to urine screens. Many factors can determine how long a particular substance is detected in a person’s urine sample; these include their age, weight, sex, metabolic rate, the amount consumed, and over what time frame. No conclusions are drawn as to when a particular substance was absorbed or how much. Drug cut-off levels help determine if it is positive or not; if there is any doubt, we recommend a lab test to confirm that. You may obtain more specific information with the results from a confirmation test. 

A full list of abused substances and detection times for urine and oral fluid can be found here.

What is a Medical Review Officer and why do we need them?

A medical review officer (MRO) is a physician that has been trained and certified to interpret and report test results. When a lab reports a specimen as negative, the MRO signs it off as negative.

The MRO is responsible for calling the person who had a positive urine sample reported and confirmed by the lab. The MRO must ask the donor if there is a reason why they were positive and ask if they have a doctor’s prescription to explain the result. In the case of marijuana or cocaine, there is virtually no justification except for the possibility of Marinol, which is a prescription drug containing marijuana, prescribed for post-chemotherapy nausea or possibly glaucoma.

When a donor claims to have a doctor’s prescription that could have caused the positive result, then the MRO must obtain a copy from the donor. If the prescription is deemed to have caused the positive result, then the MRO will sign it off as “Negative.”

If the drug cut-off levels show I’m positive, can I proclaim my innocence?

When a donor gets a positive test result for opioids after being confirmed by GC-MS testing, it may be because it contains hydrocodone, which is a prescription drug. If the donor can’t produce a prescription for this, then the MRO must report the result as positive for opioids. Conversely, if they can provide an order that satisfies the MRO, then the test with be reported as negative.

If the donor were to claim that they used a Vicks inhaler and was positive for methamphetamine, then the MRO would order a d/l isomer separation to determine if the drug present in the specimen is at least 80% l-methamphetamine. If the sample contains more than 20% d-methamphetamine, then the donor is to be considered positive for illicit methamphetamine use.

An MRO also serves to redirect the donor’s specimen to a second certified laboratory if the donor challenges the accuracy of the laboratory result. The MRO must then look at the drug test results form the second laboratory and determine if they are consistent with the findings from the first laboratory,

DOT or Federal drug tests require that an MRO report all drug results positive or negative.

We conclude that drug cut-off levels are essential to determine if a donor is presumed positive or negative. They are used as the reference or marker for determining if the result of a test is over or under the legal limit as dictated by SAMHSA.