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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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... The adsorption of purine metabolites such as uric acid, hypoxanthine, and xanthine is influenced by the urinary pH [14], which ranges from 4 to 9 [15]. Given that the pKa values of purine metabolites fall within this pH range, their protonation states fluctuate, altering their affinities for the metal surface and thereby significantly affecting their SERS spectral signatures [16,17]. ...
... To explore the effect of pH, we analyzed the SERS spectra of urine from patients with breast cancer (n = 18) and control subjects (n = 10), and compared the SERS spectra of urine at their initial pH (Figure 1a, black spectrum) with the SERS spectra of urine after we adjusted all samples to pH 5, 7, and 9 ( Figure 1a, orange, green, and blue spectra). The initial pH values of the urine samples ranged from 5 to 7, consistent with the normal physiological pH range of 4-9 [15]. The SERS spectra of urine at their initial pH were dominated by intense SERS bands corresponding to hypoxanthine (725, 1090, 1456 cm −1 ), while bands associated with uric acid at 811, 889, 1131, and 1515 cm −1 had lower-intensity. ...
... To explore the effect of pH, we analyzed the SERS spectra of urine from patients with breast cancer (n = 18) and control subjects (n = 10), and compared the SERS spectra of urine at their initial pH (Figure 1a, black spectrum) with the SERS spectra of urine after we adjusted all samples to pH 5, 7, and 9 (Figure 1a, orange, green, and blue spectra). The initial pH values of the urine samples ranged from 5 to 7, consistent with the normal physiological pH range of 4-9 [15]. The SERS spectra of urine at their initial pH were dominated by intense SERS bands corresponding to hypoxanthine (725, 1090, 1456 cm⁻ 1 ), while bands associated with uric acid at 811, 889, 1131, and 1515 cm⁻ 1 had lower-intensity. ...
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... However, the 1 H NMR chemical shifts used for metabolite assignments are sensitive to local micro-environments, such as pH, ionic strength, and matrix compositions [13]. Thus, metabolite profiles extracted from individual urine samples can vary greatly across the wide pH range [14], leading to inaccurate data interpretation [15]. ...
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... The generally accepted normal range for urine pH is 4.5-8.0; however, it is crucial to acknowledge that urine pH can vary based on several factors [15]. In instances of metabolic acidosis, urine pH tends to decrease and fall below 5, while a urine pH above 8 may indicate the presence of an infection caused by urea-splitting organisms such as Proteus mirabilis [16]. ...
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