Urine Testing Update – Preservatives for the Collection,
Transportation, and Storage of Urine Specimens
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 and Stool Collection. 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|
- The addition of preservative or application of temperature controls must occur within 4 hours of completing the collection, or an acceptable preservative must be added at the start of the collection. Urine tests that require the addition of the preservative at the start of the collection are noted by an * (asterisk) on the reference chart.
- Preservative and condition guidelines have been evaluated specifically for Mayo Medical Laboratories assays. Recommendations should only be applied to tests performed at Mayo Medical Laboratories.