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Time of collection
The time of collection relative to the time of analysis is important
because delay in analysis can result in:
- altered urine pH (increases)
- microbial proliferation (contaminants or pathogens)
- degradation of formed elements (cells and casts)
- degradation of chemical analytes (bilirubin, ketones)
If analysis cannot be performed promptly (<30 min.), refrigeration will
slow microbial growth and tends to stabilize most urine components for
up to 12 hours (rewarm to RT before analysis).
Time of day at which urine is collected can be important in some regards:
- AM (or fasting) samples tend to have:
- higher USG (decreased or no water intake)
- lower pH
- more formed elements (if longer period of formation)
- PM (or non-fasting) samples tend to have:
- lower USG
- more alkaline pH
- possibly fewer formed elements (if shorter period of formation).
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