A fresh urine specimen provides the most reliable test results. If the specimen is dilute (specific gravity <1.010), and/or the pH is >7.0, casts, white blood cells, and red blood cells may lyse. If a specimen cannot be tested within two hours of collection, it should be refrigerated at 2-8°C. If the specimen contains a preservative, it does not require refrigeration.
The specimen of choice for urinalysis is the first morning urine. The first morning urine is more concentrated and allows for the detection of substances, which may not be present in a more dilute random sample.