Collection Container for UACR Testing
For urine albumin-to-creatinine ratio (UACR) testing, use a clean, sterile plastic container made of polypropylene or high-density polyethylene without additives or preservatives.
Container Specifications
The container should meet these criteria 1:
- Material: Polypropylene or high-density polyethylene (avoid polystyrene which may bind proteins)
- Sterility: Clean and preferably sterile
- Design: Leak-proof with a lid to prevent external contamination
- pH resistance: Must withstand urine pH range without degrading
- No particle shedding: Should not release plastic microparticles into the sample
Collection Method
Use a spot (random) urine sample - timed collections are not necessary 2. The specific approach depends on patient population:
- Adults: Random spot urine collection is acceptable
- Children and adolescents: First-morning urine is preferred to avoid orthostatic proteinuria 2
- Collection technique: Midstream clean-catch urine to minimize microbial contamination 1
Critical Pre-Analytical Considerations
Sample Handling
After collection, follow these storage guidelines 2, 3:
- Refrigerate immediately at 0-4°C if not analyzed same day
- Process within 8 hours when stored at 4°C 1
- Analyze fresh or store at 4°C for up to 7 days 4
- For longer storage: Freeze at -80°C (not -20°C) - storage at -20°C causes 34% loss of albumin over 12 months 3
- Avoid repeated freeze-thaw cycles 2
Important Caveats
Do NOT use:
- Blood collection tubes (e.g., EDTA tubes, serum separator tubes) - these are designed for blood, not urine
- Containers with preservatives or additives unless specifically required for extended collection times
- Containers that may bind proteins or shed particles
Patient preparation 2:
- Avoid vigorous exercise for 24 hours before collection
- Document any medications, recent meals, or unusual circumstances
Laboratory Reporting Standards
The laboratory should report 2, 4:
- UACR in mg/g creatinine (or mg/mmol in some regions)
- Report to 1 decimal place
- Reference range: ≤30 mg/g creatinine is normal
- Both albumin and creatinine concentrations in addition to the ratio
Common Pitfalls to Avoid
- Using blood collection tubes: These contain anticoagulants (EDTA, heparin) or gel separators inappropriate for urine
- Storage at -20°C: Results in significant albumin degradation 3
- Delayed refrigeration: Allows bacterial growth and protein degradation 1
- First-void urine in children: May be contaminated; use midstream collection 1
The key principle is simplicity: a plain, clean plastic urine container with prompt refrigeration provides accurate UACR results without the complexity of specialized collection tubes or additives.