Best Practice: Tips for Urine Analysis
Q: We cannot guarantee that urine samples are always the required volume, kept refrigerated, and processed within 2 hours of collection. Is there any alternative?
A: A majority of urine specimens are collected either in physicians' offices or at hospitals. Throughout the past decade, testing practices have changed rapidly and an increasing number of specimens are transported to remote or core laboratories. The laboratories are faced with transport effects on the specimens. BD recommends collecting urine specimens in the BD Vacutainer® Plus Plastic Conical Urinalysis Preservative Tube because specimen integrity is maintained for up to 72 hours without refrigeration.
Instructions for Use
In the event that a urine preservative system is not used, NCCLS recommends that the urinalysis testing be performed within 2 hours of specimen collection. If testing cannot be performed within this time frame, refrigeration (2 to 8° C) is adequate for some chemical components (exceptions being bilirubin and urobilinogen). At these storage temperatures, the specimen can precipitate amorphous urates or phosphates, which obscure the microscopic field. The length of time refrigeration can serve as a preservative has not been determined.1 NCCLS1 also recommends, "If 'urine preservation' systems are used, they should first be evaluated by the laboratory".
It is generally accepted that after standing 2 hours at room temperature, the chemical composition of unprocessed urine changes, and formed elements begin to deteriorate.
The following are changes that may occur:
Cells and casts disintegrate in dilute urine (SG < 1.010) and urine that becomes alkaline upon standing (pH > 7.0)
BD performed evaluations of the BD Vacutainer® Plus Plastic Conical Urinalysis Preservative Tube stored at room temperature (RT). The tube was compared to the BD Vacutainer® Plus Plastic Conical Tube (RT) at initial time and at 72 hours after tube fill for urine dipstick chemistries. The preservative tube demonstrated some urine analyte results outside the normal reference ranges. Statistical analysis for urine dipstick chemistries showed that over 72 hours there were no clinically significant differences observed between the BD Vacutainer Plus Plastic Control Tube at RT and the BD Vacutainer Plus Plastic Conical Urinalysis Preservative Tube.4, 5
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