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 Cut-Off levels?
This is the point at which a test is either a presumed positive or negative. A positive result is when the drug detected is above the set level for that drug. For example, if cocaine was detected, the level detected 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 if a drug was detected. This is evident because there will be 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 positive, to know how high, 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 positive or negative; when confirmed by GC-MS (Gas Chromatography-Mass Spectrometry) at a SAMHSA certified laboratory will report what drug was found and its detected level.
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
|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
|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 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.