When a DOT result comes back as something other than a clean negative or positive, it can be confusing. Here is what the lab terms mean.
Dilute
A dilute specimen is real urine that is watered down — often from drinking a lot of fluid. A negative-dilute is usually still a valid negative, though the employer may be allowed to require a recollection. A positive-dilute is treated as a positive.
Substituted and Adulterated
- Substituted: the sample does not have the characteristics of human urine (it was swapped)
- Adulterated: a foreign substance was added to defeat the test
Both are handled as a refusal to test under DOT rules, with the same serious consequences as a positive.
What to Do
Employers should rely on the MRO's guidance for each result code. The MRO determines whether a recollection (sometimes observed) is required.
Frequently Asked Questions
Is a dilute result a failed test? A negative-dilute is generally a valid negative. A positive-dilute is a positive. Policy may call for a recollection on a negative-dilute.
What happens with a substituted or adulterated result? Under DOT rules these are treated as a refusal to test, carrying the same consequences as a positive.
Can I avoid a dilute result? Avoid overhydrating right before a test. The MRO and collector handle the rest.
Let Test Pro Handle It
Test Pro LLC in Kent, WA helps owner-operators, motor carriers and employers stay compliant across Washington and beyond — drug and alcohol testing, random pools, IFTA, filings and driver files. Call (206) 518-2097 or book an appointment. Questions first? Contact us.