Why are there drug cut-off levels with drug tests
○ 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 to 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 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.
The image above tells us a drug of abuse was detected. This is evident because there is no line in the test window (T) for Cocaine, this is called a presumed positive. The metabolite of cocaine has been detected at a level higher than 300 ng/ mL. Anything higher 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 utilizing a technique called Gas Chromatography-Mass Spectrometry and report it with a level. In this case, it was 2100 ng/mL.
NOTE: Presumed positive test samples should be sent for confirmation to a SAMHSA approved lab.
○ Should I use a laboratory if the drug cut-off levels show the result is positive?
The short answer is YES. Whenever the screening levels are exceeded the test is presumed positive. But substance screening only tells you if the test is presumed positive or negative; when confirmed by GC/MS (Gas Chromatography/Mass Spectrometry) at a SAMHSA certified laboratory will report what drug was found and by how much.
GC/MS confirmation is very specific when looking for drugs and 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.
All FDA cleared drug screening tests have to adhere to strict cut-off levels as can be seen in the chart below.
Source: National Institute on Drug Abuse (NIDA).
Urine Cut-off Levels
|Test||Calibrator|| Cut off |
|Cocaine 150 (COC)||Benzoylecgonine||150|
|Ecstasy (MDMA)||3,4- Methylenedioxymethamphetamine||500|
|Marijuana (THC)||1-nor-Δ9 -THC-9-COOH 1||50|
|Methamphetamine 500 (MET)||D-Methamphetamine||500|
|Tricyclic Antidepressants (TCA)||Nortriptyline||1000|
Oral Saliva Cut-off Levels
|Test||Calibrator|| Cut off |
|Marijuana (THC)||1-nor-Δ9 -THC-9-COOH 1||25|
|Ecstasy (MDMA)||3,4- Methylenedioxymethamphetamine HCI||100|
○ What are the detection times?
Detection times are estimates and apply only to urine screens. Many factors can determine how long a particular substance can be detected in a person, 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 consumed 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 drugs and detection times for urine and oral fluid are available here.
○ What is a Medical Review Officer?
A medical review officer (MRO) is a physician that has been trained and certified to interpret and report test results. If the 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 the very rare possibility of Marinol, which is a prescription drug containing marijuana that can be prescribed for post-chemotherapy nausea or possibly glaucoma).
When a 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 from 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 result was “Negative”.
○ Proclaiming your innocence if the result is over the drug cut-off levels.
When a donor gets a positive test result for opioids after being confirmed by Lab 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 are able to provide a prescription and it 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 specimen 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 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.
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.