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 a 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.