DOT Rule 49 CFR Part 40 Section 40.89
Subpart F - Drug Testing Laboratories
§ 40.89 What is validity testing, and are laboratories required to conduct it?
(a) Specimen validity testing is the evaluation of the specimen to determine if it is consistent with normal human urine. The purpose of validity testing is to determine whether certain adulterants or foreign substances were added to the urine, if the urine was diluted, or if the specimen was substituted.
(b) As a laboratory, you must conduct validity testing.
[65 FR 79526, Dec. 19, 2000, as amended at 66 FR 41951, Aug. 9, 2001; 73 FR 35970, June 25, 2008]