Understanding an Invalid Drug Test: 7 Questions to Follow Up With

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5 September 2023

Understanding an Invalid Drug Test: 7 Questions to Follow Up With

The costs of illicit drug use in the workplace are well known. Still, a reliable workplace drug and alcohol policy can help you decrease employee turnover and absenteeism, increase productivity and safety and reduce your risks. Of course, for Department of Transportation (DOT) covered employers, drug testing is mandatory.

The rate of positive tests continues to climb, increasing over 5% for all illicit drugs since 2004 and increasing over 7% over the same time period for cannabis. Responding to a negative or positive drug test is easy. But what do you do when a test comes back as inconclusive or invalid?

Here are seven questions you should ask that can help you decide the best course of action to take.

1. Why was the test declared invalid?

The first question you should ask is the reason for the invalid drug test. A test can be marked invalid for numerous reasons that include:

The reason for the invalid drug test can inform the next steps. For example, an insufficient testing sample is very different from a deliberate substitution or adulteration of a sample.

2. Has the specimen been retested?

Retesting can be an option if there is a possibility of a laboratory error or an insufficient sample. The lab and the Medical Review Officer (MRO) will request a retest. The donor can also request a retest if the request is made within three days of the results being made available.

Typically, the retesting occurs at a second Health and Human Services (HHS) approved lab. The first lab will either send the second lab the remainder of the sample or, if split testing was done, they will forward the second sample.

If there is an insufficient quantity of the original sample or the sample was lost at the originating lab, the MRO can then request that the donor provide a second sample under direct observation. This means that a laboratory employee will directly observe the donor while the sample is produced.

3. Have validity tests been conducted at the reporting lab?

Although urine testing is a common and reliable method for drug testing, it is not entirely foolproof. Errors can occur during collection or at the lab but can also indicate a deliberate attempt to interfere with the test. The identification of an unidentified adulterant or an unknown interfering substance, abnormal physical characteristics, or an endogenous substance at an unusual concentration can all indicate an issue with the test.

Examples of these are:

In addition to screening for drugs, laboratories run validation tests to test for all of these abnormalities. DOT, in particular, mandates validation testing for all drug collection. For example, labs must determine the pH and creatine concentration and specific gravity if creatine levels are less than 20 mg/dL. If abnormal physical characteristics, reactions or responses are observed, then additional validation tests must be conducted.

4. Has the MRO interviewed the test taker?

If the laboratory and MRO decide that no further testing of the sample is necessary, then the MRO will contact the employee to inform them that the test results were invalid. They will also interview the employee to determine if there is a medical explanation for the invalid test. Part of this process requires the employee to provide a list of medications they are currently taking. If the employee can provide a legitimate reason that explains the invalid test, the MRO declares that although the test is cancelled, no further testing is required. If no appropriate explanation is offered, then the MRO will report the test cancelled, and the employee will be required to take a second test, this time under the direct observation of a laboratory employee.

5. Did the employee admit to adulterating the sample?

In some cases, an employee will openly admit to the MRO that they adulterated or substituted the sample or that they used illegal drugs. If they admit to adulterating or substituting the sample, the MRO reports it as a refusal to test. If they admit to using illicit substances, the MRO will immediately report it to the Designated Employer Representative (DER) at your workplace.

6. What are company procedures for return to work on an invalid test?

As always, a clear company policy that addresses invalid tests and, in particular, return to work following an invalid test, can protect everyone. For pre-employment screening, it is a good idea to require a second test. Inform your potential employee of the need to retest and request that they avoid drinking too much water before the next test as a second diluted result could preclude you from hiring them.

For existing employees, again, a second test should be required alongside an interview to determine if there are other possible reasons for the invalid test. If an employee is using prescription medications and is in a safety-sensitive position, you will need to review your procedures and determine if accommodation is necessary. If an employee refuses to retest, you may terminate the employee, but it is a good idea to have this recorded in your company policy.

7. What are DOT rules regarding a return to work on an invalid test?

DOT rules regarding a return to work on an invalid test are clear and provide a useful template for non-DOT governed employers to follow.

If the test is invalid, but the MRO determines prescription drugs may have interfered, the employee may return to work as long as these drugs do not interfere with their ability to do the job safely.

If the test is invalid and a retest is ordered, the results of the second test will dictate the appropriate return to work policy.

If the employee refuses a retest, they are subject to termination for a refusal to test.

The Takeaway

Invalid test results can be confusing and frustrating for both employers and employees. Asking the right questions and understanding the procedures as well as the checks and balances that are in place to ensure drug testing validity can help.