Everything to know about cut-off levels in drug testing

Have you ever wondered about what decides the negative and positive results of a drug test? It’s as simple as the routine biochemical tests that happen in the laboratory. Recall the reference values that you observe on your test reports. Similar is the case with drug testing results. The reference values or cut-offs determine the drug testing results.


Go through this article to get every answer!

What is a cut-off in drug testing?

“Cut-off” in drug testing is a value that can help an analyzer to clearly separate the negative and positive results. If the subject who has been tested for drugs or alcohol is detected with an amount of the same below the cut-off values the donor is considered to be safe for the work environment. This means that the result is considered to be negative. But if it exceeds the cut-off, the results are considered positive.

Let’s look at some examples for such cut-offs:

0.08BAC: More than 80mg of alcohol for 100ml of blood is considered to be a positive result. Thus, if you undergo a breathalyzer random drug test and get detected with less than this amount of alcohol, the results will be considered negative.

Similarly, there are different cut-offs decided for random and onsite drug testing related to cannabis, marijuana, Amphetamines, Phencyclidine, Codeine, Morphine, etc.

Methods of determining drug testing cut-offs

It is crucial that the cut-off threshold used in every hair test is high enough to rule out any potential contamination, but still low enough to be entirely confident that the donor has abstained from substance use due to a negative outcome. Consequently, cut-offs should be measured accurately. We can thus confirm intentional substance use if a random or onsite drug test shows an amount of a drug above the cut-off.

The cut-offs for urine or fluid drug tests at Corpus Christi are designed in a way that they have dual cut-off levels. Here are their specifications:

  • Screening cut-off: This decides the necessity for a confirmation test. In other words, it is the cut-off limit that is set for a primary screening test. If the drug or alcohol concentration detected in the sample is more than the cut-off, it is sent for a confirmatory test. Otherwise, the result is declared as negative.
  • Confirmation cut-off: It is the cut off decided for the confirmatory drug test. If the sample tests for a concentration of drugs that is more than the limit, the result is finally declared as positive.

Such cut-offs mean that we will increase the recognition of existing drug use. They also suggest that the monitoring of medications used in earlier times can be reduced and the probability of outcomes caused by foreign contamination can be minimized. What is critical to know, indeed, is that a cut-off is not a single number that exists around the board-it is a variety of factors that change based on multiple variables.

Can cut-offs differ?

Yes! The drug testing cut-offs can differ among the laboratories even if they belong to the same state. The drug testing in Corpus Christi has varying cut-offs based on the following factors:

A. The difference in samples:

No single cut-off applies to all the drug testing procedures. For instance, when a drug is tested through hair as a sample the cut-off rules will be as per the ones recommended by the Hair testing Society of that state. Similarly, the recommended cut-offs for the same drug in urine test differed from those in blood tests.

Fact: The cut-offs for drugs and alcohol in hair sample is generally lower than the ones for blood, urine, oral fluid or breath samples.

B. The difference in analytes:

For the same sample, the cut-offs for different drugs vary according to the prior research conducted by the organizations of that particular state. The cut-off limit for cocaine concentration in hair differs from that of THC metabolite. The drug testing centers are well equipped with all the values for screening as well as confirmatory tests.

C. Laboratory rules:

Laboratories follow the cut-offs recommended by the state or some drug testing government authorities. Depending on their reference of cut-off values, and methods of drug testing, the values of both screening and confirmation cut-offs may vary. But this is a rare event. Generally, all the laboratories follow a uniform cut-off value. However, it is recommended to choose a state-accredited laboratory for onsite or random drug testing for the better encounter of substance abuse among your employees, or children.

How does the lab deal with uncertain measurements?

There are situations when the laboratories need to make some assumptions based on the drug testing outcomes. This may sometimes manipulate the concentration values and make them cross the cut-off limits. Such a phenomenon is rare and in such cases, the laboratory experts clearly mention the reason behind their assumption in the drug testing reports.

Thus, every uncertainty related to interpretation or measurements from the side of the laboratory is well explained so that the employer, authorities, or parents can get a clear idea about the results.

Importance of cut-offs in drug testing

Cut-offs are extremely important when it comes to drug testing. Here are the reasons for the same:

  1. a. They help determine the necessity for a confirmation test.
  2. b. They can help an employer save the revenue that goes into unnecessary on-site confirmatory drug tests.
  3. c. It can clearly define negative and positive drug testing results. Thus, it indicates the safety of a worker in the organization.

Wrapping it up

Cut-offs are extremely important for detecting positive and negative results of onsite as well as random drug testing. Thus, it is important to know everything mentioned above before going for a drug test. You can contact us 24/7 Onsite for more information.