Published: Journal of Analytical Toxicology, ISSN 0146-4760, Volume 31, Number 8, October, pp.486-496

Urine pH: the Effects of Time and Temperature after Collection
Janine D. Cook[1], Kathy A. Strauss[2], Yale H. Caplan[3], Charles P. LoDico[4], and Donna M. Bush[4]
[1]Department of Pathology, Mercy Medical Center, Baltimore, Maryland 21202
[2] School of Medicine, Department of Epidemiology, University of Maryland Baltimore, Baltimore, Maryland 21201
[3]National Scientific Services, Baltimore, Maryland 21208
[4]Division of Workplace Programs, Center for Substance Abuse Prevention, Substance Abuse and Mental Health Services Administration, One Choke Cherry Road, Rockville, Maryland 20857

The Mandatory Guidelines for Federal Workplace Drug Testing Programs provide criteria for specimen validity testing, including urine pH cut-offs, to report a urine specimen as adulterated or invalid. Since the urine pH criteria for invalid classifications, ≥ 3 and < 4.5 or ≥ 9 and < 11, became effective in November 2004, a number of specimens with results within the upper invalid limits, typically in the range of 9.1 to 9.3, have been reported with no evidence of adulteration. This study evaluated the hypothesis that these pH findings were the result of exposure to increased environmental temperatures during specimen standing and transport. Indeed, increased storage temperatures were associated with increased urine pH, with the magnitude of the change related to both storage time and temperature. The pH values of specimens stored at –20°C are relatively stable, whereas pH results > 9 are achieved at storage temperatures of room temperature or higher. It is noteworthy that no condition(s) produced a specimen with a pH > 9.5. Degradation of nitrogenous urine analytes is most likely responsible for the noted increases in pH. These findings are intended to supplement information used by the Medical Review Officers who are responsible for interpreting such marginally invalid pH results.

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