Uric acid is not part of the validity tests conducted on DOT specimens. With DOT testing, regulations and protocol adherence is a must. Failure to follow the regulations can result in serious sanctions imposed by the Agency, including the loss of the labs certification to conduct DOT testing. And since DOT tests are a labs bread and butter, this would spell the end for them as a business.

Below is the regulation that outlines the what validity tests must be performed on the urine sample:

Subpart F - Drug Testing Laboratories

§ 40.91 What validity tests must laboratories conduct on primary specimens?

As a laboratory, when you conduct validity testing under §40.89, you must conduct it in accordance with the requirements of this section.

(a) You must determine the creatinine concentration on each primary specimen. You must also determine its specific gravity if you find the creatinine concentration to be less than 20 mg/dL.

(b) You must determine the pH of each primary specimen.

(c) You must perform one or more validity tests for oxidizing adulterants on each primary specimen.

(d) You must perform additional validity tests on the primary specimen when the following conditions are observed:

(1) Abnormal physical characteristics;

(2) Reactions or responses characteristic of an adulterant obtained during initial or confirmatory drug tests (e.g., non-recovery of internal standards, unusual response); or

(3) Possible unidentified interfering substance or adulterant.

(e) If you determine that the specimen is invalid and HHS guidelines direct you to contact the MRO, you must contact the MRO and together decide if testing the primary specimen by another HHS certified laboratory would be useful in being able to report a positive or adulterated test result.

[65 FR 79526, Dec. 19, 2000, as amended at 69 FR 64867, Nov.9, 2004]

Updated: Thursday, March 14, 2013

Source: DOT Rule 49 CFR Part 40 Section 40.91 | Department of Transportation
And here is the criteria that must be applied when determining a "non-human" (aka 'substituted') specimen:

§ 40.93 What criteria do laboratories use to establish that a specimen is dilute or substituted?

(a) As a laboratory you must consider the primary specimen to be dilute when:

(1) The creatinine concentration is greater than or equal to 2mg/dL but less than 20 mg/dL, and

(2) The specific gravity is greater than 1.0010 but less than 1.0030 on a single aliquot.

(b) As a laboratory you must consider the primary specimen to be substituted when the creatinine concentration is less than 2 mg/dL and the specific gravity is less than or equal to 1.0010 or greater than or equal to 1.0200 on both the initial and confirmatory creatinine tests and on both the initial and confirmatory specific gravity tests on two separate aliquots.

[65 FR 79526, Dec. 19, 2000, as amended at 69 FR 64867, Nov.9, 2004]

Updated: Thursday, October 25, 2012

Source: http://www.dot.gov/odapc/part40/40_93

And here is the link to the rest of the DOT regulations in their entirety. A must-read for anyone facing a DOT test:
http://www.dot.gov/odapc/part40

And yes, the regulations are current.