Gram-negative bacteria can cause:
(1) conversion of urinary nitrate to nitrite
(2) increase in pH, almost always < 9.5 (due to breakdown of urea by bacterial urease)
A pH >= 9.5 indicates that something else is happening.
A pH > 11 is considered adulterated.
A urine with a pH 9.0 to 11.0 is considered invalid.
A urine nitrite concentration >= 500 µg/mL (50 mg/dL) is considered adulterated. A nitrite concentration of 200 to 499 µg/mL is considered invalid.
If a positive result is found with either test, then the urine sample should be screened for a urinary tract infection or bacterial overgrowth, which may include:
(1) bacterial culture
(2) urine microscopic for white blood cells and bacteria
(3) urine dipstick
(4) a history of the specimen being left unrefrigerated in warm weather
(5) clinical evidence of an untreated urinary tract infection in the patient
If the urine specimen has been frozen prior to testing then resolution is more problematic. Molecular techniques may be required. Tests like PCR may be so sensitive that there is a risk for false positive results. In a non-DOT drug test it may be easier to have the patient screened for a UTI or to do hair testing.
