What Is an Invalid Drug Test Result?

An invalid result is the result an HHS-certified laboratory reports, using criteria set by the U.S. Department of Health and Human Services (HHS), when a positive, negative, adulterated or substituted result cannot be established for a specific drug or specimen validity test (49 CFR 40.3). An invalid result is not a positive result and is not, by itself, a refusal to test.

What makes a urine result invalid. Under Section 3.9 of the HHS Mandatory Guidelines for urine, a laboratory reports a primary (A) specimen as invalid when, among other criteria:

• creatinine and specific gravity results are inconsistent with each other
• the pH is equal to or greater than 4 and less than 4.5, or equal to or greater than 9 and less than 11
• tests show the possible presence of nitrite, chromium (VI), a halogen, glutaraldehyde, a surfactant or an oxidizing adulterant at levels set in the guidelines
• interference occurs on the initial drug tests on two separate aliquots, or on the confirmatory drug test on two separate aliquots and the laboratory cannot identify the interfering substance
• the specimen's physical appearance could damage the laboratory's instruments, or the primary (A) and split (B) specimens clearly look different

Oral fluid. Section 3.8 of the HHS oral fluid guidelines uses a shorter list: interference on the initial drug tests, or on the confirmatory drug test when the laboratory cannot identify the interfering substance, a physical appearance that could damage instruments, clearly different primary and split specimens, or a specimen validity test showing the specimen is not valid for testing.

What happens next. In DOT testing, the Medical Review Officer (MRO) reviews the invalid result with the laboratory and the employee under 49 CFR 40.159. The test is reported as cancelled, and a cancelled test is neither a positive nor a negative test (49 CFR 40.3). Whether a directly observed recollection follows depends on whether the employee has an acceptable medical explanation. The FAQ on what an MRO does when a result is invalid covers those steps. An invalid result differs from a dilute result, which the FAQ on DOT dilute drug test results explains, and a directly observed recollection is described in the FAQ on observed collections.

Pending proposal. HHS has proposed changes to the urine guidelines that would raise the lower bound of the invalid pH range from 9.0 to 9.5 (FR 2026-22122). The proposal is not final, and the current criteria apply.