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 increases the urine pH. 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.

The "run-over" phenomenon may occur if excess urine remains on the strip. The protein area, adjacent to the pH area, contains an acid buffer which may "run-over" the pH portion resulting in an acid reading on a neutral or alkaline urine.