|Values are valid only on day of printing.|
The Department of Laboratory Medicine and Pathology at Mayo Clinic initiated an extensive study to determine the stability of various analytes under different preservative conditions. The validation of each analyte’s stability in urine includes testing 10 specimen pools over 4 time periods (Days 0, 1, 3, 7) for each condition or preservative. The selection of the preferred condition or preservative and definition of rejection criteria for each analyte stem from these studies.
This study not only allows for the use of temperature controls to preserve several analytes, but also enables laboratories to maximize the number of tests that can be performed on a single 24-hour collection.
A reference chart indicating preferred and acceptable preservative options has been constructed from this information. It is available on the Web site by accessing Urine Preservatives. Specific specimen preservative requirements are listed for each analyte under “Specimen Requirements” at MayoMedicalLaboratories.com.
The conditions and concentrations of urine preservatives are defined for 24-hour collections as follows:
|Ambient||Room temperature (21°–25° C)|
|6N HCI||30 mL per 24-hour collection|
|50% Acetic Acid (Supply #T008)||25 mL per 24-hour collection|
|Na2CO3 (crystals) (Supply #T272)||5 g per 24-hour collection|
|Toluene||30 mL per 24-hour collection|
|6N HNO3||15 mL per 24-hour collection|
|Boric Acid (crystals) (Supply #T473)||10 g per 24-hour collection|
|Thymol (10% isopropanol)||10 g per 24-hour collection|