The urine specimen should be freshly voided. Urine is an ideal medium for the proliferation of bacteria due to the large amount of urea present. These bacteria metabolize urea, producing ammonia that causes the urine pH to become more alkaline. If there is a delay before performance of the test, the sample should be refrigerated. This will:

• Prevent urease-producing organisms, such as Proteus and Pseudomonas, from converting urine urea to ammonia, which results in an increased pH.
• Prevent loss of CO2 which increases pH to the alkaline range.