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An adulterated specimen contains a substance that is not expected in human urine, or an endogenous substance at a level that is not normal. A substituted specimen has creatinine and specific gravity values so far outside normal ranges that it is not consistent with human urine (49 CFR 40.3).

When the MRO verifies an adulterated or substituted result, it is a refusal to test (49 CFR 40.191), with the same consequences as a verified positive: removal from safety-sensitive functions and referral to a SAP. The employee may request a split specimen test.