○ Why does a drug test 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 to recommendations 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 at a concentration that is lower than the defined cut-off level.
○ What are cut-off levels?
This is the point at which a test is either a presumed positive or negative. A positive test is when the drug detected is above the set level for that drug. For example, if cocaine was detected, the level found will be above 300 ng/ml. Cut-off levels vary depending on which drug is tested. (see chart below)
The results from a test are displayed in panels on the face of the device. In the image below, each panel shows two colored lines, 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.
NOTE: Presumed positive test samples should ;be sent for confirmation to a SAMHSA approved lab.
The image above tells us Cocaine was detected, it indicates this because there is no line in the test window (T). This is called a ‘presumed positive‘, where the metabolite of cocaine was detected at a level greater than 300 ng/ mL. Anything greater than 300 ng/mL is considered positive but to know by how much, the sample has to be confirmed by a lab; they would test the sample again and report the level by means of gas chromatography – gas spectrometry.
○ Should I use a laboratory if the drug cut-off levels show a presumed positive?
The short answer is YES. Whenever the screening levels are exceeded the test is presumed positive. But all drug screening tests only tell you the test is either presumed positive or negative. The urine sample, when confirmed by GC/MS (Gas Chromatography/Mass Spectrometry) at a SAMHSA certified laboratory, will report what drug was found and by how much. This is compared to the standard drug cut-off levels.
GC/MS confirmation is very specific when looking for drugs and also quantifies the target metabolite with a number. GC/MS confirmations sent to a certified laboratory will also stand up in the court of law if the test result is challenged by a donor.
Screen cut-off levels for rapid urine tests conform to the chart below as per National Institute on Drug Abuse (NIDA) recommendations.
|Drug||Identifier||Test cut-off||Lab cut-off|
|Amphetamines||(AMP)||1000 ng/mL||500 ng/mL|
|Barbiturates||(BAR)||300 ng/mL||200 ng/mL|
|Buprenorphine||(BUP)||10 ng/mL||5 ng/mL|
|Benzodiazepines||(BZO)||300 ng/mL||200 ng/mL|
|Cocaine 150||(COC)||150 ng/mL||150 ng/mL|
|Cocaine||(COC)||300 ng/mL||150 ng/mL|
|Ecstasy||(MDMA)||500 ng/mL||250 ng/mL|
|Marijuana||(THC)||50 ng/mL||15 ng/mL|
|Methamphetamine 500||(mAMP)||500 ng/mL||500 ng/mL|
|Methamphetamine||(mAMP)||1000 ng/mL||500 ng/mL|
|Methadone||(MET)||300 ng/mL||200 ng/mL|
|Morphine||(MOP)||300 ng/mL||150 ng/mL|
|Opiates||(OPI)||2000 ng/mL||2000 ng/mL|
|Oxycodone||(OXY)||300 ng/mL||100 ng/mL|
|Phencyclidine||(PCP)||25 ng/mL||25 ng/mL|
|Propoxyphene||(PPX)||300 ng/mL||200 ng/mL|
|Tricyclic Antidepressants||(TCA)||1000 ng/mL||1000 ng/mL|
Note: Do not compare Drug Screen cut-off levels and Lab drug cut-off levels as the testing methodology are different.
○ What are detection times?
Detection times are estimates and apply only to urine drug screens. There are many factors that can determine how long a particular drug can be detected in a person, these include; their age, weight, sex, metabolic rate, the amount of drug consumed and over what time frame. No conclusions can be drawn as to when a particular drug was taken or how much was consumed with urine drug screens. If you get a positive from a drug screen we recommend a lab test, which we can arrange. More specific information can then be obtained with the results of a confirmation test. A full list of drugs and detection times for urine and oral fluid can be found here.
|Propoxyphene||6 hours to 2 days|
|Hallucinogens||Lysergic Acid||1-5 days|
|Marijuana and Cannabinoids||Single Use – 2-7 days|
30 to 45 days
|Phencyclidine||Single Use – 1 week|
|Stimulants||Cocaine||Single Use – 3 days|
|Amphetamines||Single Use – 3 days|
|Methylene-2, 4 dioxy-methamphetamine||Single Use – 24 hours|
|Methamphetamine||Single Use – 48 hours|
|Alcohol & Metabolites||Ethanol||Less than 1 day|
|Methanol||Less than 1 day|
|Isopropanol||Less than 1 day|
|Acetone||Less than 1 day|
|Ethylene Glycol||Less than 1 day|
|Benzodiazepines||Diazepam||Single Use – Not detected|
|Oxazepam||Single Use – Not detected|
|Alprazolam||Single Use – Not detected|
|Clonazepam||Single Use – Not detected|
|Chlordiazepoxide||Single Use – Not detected|
|Lorazepam||Single Use – Not detected|
|Ketamine||Less than 72 hours|
○ What is a Medical Review Officer?
A medical review officer (MRO) is a physician that has been trained and certified to interpret and report drug screen results. If the lab reports a specimen as negative, the MRO signs off on the negative drug screen result.
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 doctors prescription to explain the result. In the case of marijuana or cocaine, there is virtually no justification (except the very rare possibility of Marinol, which is a prescription drug containing marijuana that can be prescribed for post-chemotherapy nausea or possibly glaucoma).
If the donor claims to have a prescription for a drug that could have caused the positive result, then the MRO must obtain a copy of the prescription form the doctor or the pharmacy that issued the prescription. If the prescription is deemed to have caused the positive result, then the MRO reports that the drug screen was “Negative”.
Example: If the donor were to claim that they had a methamphetamine positive because they used a Vicks inhaler, 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 specimen contains more than 20% d-methamphetamine, then the donor is to be considered positive for illicit methamphetamine use.
If a donor is positive for opiates and confirmed by GC/MS to contain hydrocodone and the donor’s doctor or pharmacist produces a prescription for codeine, oxycodone or some opiate drug other than hydrocodone, then the MRO must report the drug screen as positive for opiates.
An MRO also serves to redirect the donor’s specimen to a second certified laboratory in the event that 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 including negative results.
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