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.
First-morning urine is the specimen of choice for urinalysis. It is more concentrated and allows for detecting substances that may not be present in a more dilute random sample.
