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DOT Rule 49 CFR Part 40 Section 40.179

Subpart H - Split Specimen Tests

§ 40.179 What does the second laboratory do with the split specimen when it is tested to reconfirm an adulterated test result?
(a) As the laboratory testing the split specimen, you must test the split specimen for the adulterant detected in the primary specimen, using the confirmatory test for the adulterant and using criteria in § 40.89 or § 40.93, as applicable and confirmatory cutoff levels required by the HHS Mandatory Guidelines.
(b) In addition, if the test fails to reconfirm the adulterant result reported in the primary specimen, you may send the specimen or an aliquot of it for testing at another HHS-certified laboratory that has the capability to conduct another reconfirmation test.
[73 FR 35973, June 25, 2008, as amended at 88 FR 27646, May 2, 2023]