With the prevalent use of adulterants to mask known positive drug tests, a number of mechanisms have been developed to check potentially invalid specimens. The simplest adulterant-detection systems check urine samples that deviate from normal ranges of temperature, specific gravity, pH, and creatinine. The temperature for normal urine samples should be 90.5-98.9°F. The specific gravity should be 1.005-1.030, and pH should be 4.0-10.0. The creatinine concentration should be 20-400 mg/dL. Dilution of urine as a result of excess water consumption also lowers the concentration of creatinine in the urine. Adulteration with sodium chloride at a concentration necessary to produce a false-negative result always produces a specific gravity over 1.035. Household vinegar and concentrated lime juice cause urine to turn acidic.
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