No. A newly collected negative test does not replace or overturn an MRO-verified positive, adulterated, or substituted result.

The only retest DOT allows is the split specimen: the second bottle sealed at the original collection. The employee asks the MRO, verbally or in writing, within 72 hours of being told of the verified result (49 CFR 40.171). The split is sent to a different HHS-certified laboratory.

If the split does not reconfirm the result, the MRO cancels the test. The employer may not require the employee to pay for the split test in advance, but may seek reimbursement.