What is the proper method for storing urine?

Proper Methods for Storing Urine

Urine samples should be stored at 0-4°C and processed within 8 hours of collection to avoid bacterial growth, cell lysis, molecular degradation, and sediment formation. 1

Collection Considerations

Collection Method

• Use midstream collection with cleansing for most accurate results and lowest contamination rates 1
• Collect midstream urine in a clean, leak-proof container that won't bind urinary components or shed particles 1
• Use sterile containers when studying microbial components or when contamination is a significant concern 1
• Avoid cardboard containers as they may produce false positive nitrite results in dipstick testing 2

Container Specifications

• Use containers made of high-density polyethylene or polypropylene 1
• Ensure containers are:
  • Clean and leak-proof
  • Urine pH-range resistant
  • Free from materials that could shed particles
  • Preferably with a lid to prevent external contamination 1

Short-Term Storage (Before Processing)

Temperature Control

• Keep freshly collected urine at 0-4°C (refrigerated) if not processed immediately 1
• Process within 8 hours of collection for optimal results 1
• Be aware that cold temperatures (2-4°C) may cause formation of uromodulin polymers that can trap extracellular vesicles 1

Preservatives for Longer Collection Times

• For 24-hour collections or when processing within 8 hours isn't possible:
  • Consider adding preservatives such as sodium azide to prevent microbial growth 1
  • For specific protein analysis, protease inhibitors may be beneficial for certain proteins (e.g., NKCC2) 1
  • For RNA analysis, consider RNase inhibitors, though systematic studies are limited 1

Long-Term Storage

Freezing Recommendations

• For long-term biobanking:
  • Aliquot samples and freeze at -80°C 1
  • Even moderate freezing at -22°C without preservatives can maintain stability of many clinical chemistry parameters for over 10 years 3

Stability of Analytes

• Many urinary analytes remain stable during long-term frozen storage, including:
  • Creatinine, urea, iodine, nitrogen
  • Sodium, potassium, magnesium, calcium
  • Ammonium, bicarbonate, citric acid, uric acid 3

Common Pitfalls to Avoid

1. Delayed processing without refrigeration: Urine left at room temperature for more than 4 hours can lead to overgrowth of both clinically significant and contaminating flora 1

2. Improper container selection: Cardboard containers can cause false positive nitrite results in dipstick testing 2

3. Prolonged warming during thawing: Can promote microbial growth; thaw samples carefully and avoid extended periods at room temperature 1

4. Multiple freeze-thaw cycles: Can diminish quality and quantity of certain urinary components 1

5. Failing to record collection details: Important to document collection method, time, volume, and any additives used 1

For clinical applications requiring the highest accuracy, following these storage guidelines will help maintain sample integrity and ensure reliable test results.