What Does an Invalid DOT Drug Test Result Mean?

An invalid result is defined in 49 CFR 40.3 as the result reported by an HHS-certified laboratory "when a positive, negative, adulterated, or substituted result cannot be established for a specific drug or specimen validity test." Under 49 CFR 40.90, the laboratory applies the invalid result criteria in the HHS Mandatory Guidelines and reports the reason the result is invalid.

Under 49 CFR 40.159, the MRO first discusses the result with a laboratory certifying scientist to decide whether the specimen should be tested at another HHS-certified laboratory. If no further testing is needed, the MRO contacts the employee, asks about medications and determines whether there is a medical explanation for the invalid result.

Under 49 CFR 40.159(a)(4) and (a)(5), the MRO cancels the test in either case. With an acceptable explanation, no further action is required unless a negative result is needed, as in pre-employment, return-to-duty and follow-up tests. Without one, the MRO reports that a second collection must take place immediately under direct observation. If the employee admits adulterating or substituting the specimen, the MRO reports a refusal to test.

A related result is explained in What Does a Cancelled DOT Drug Test Mean?.

Employers and employees can search the MyDrugTesting.com directory by location and service to find collection sites, laboratories and MROs.