24-Hour Urine Collection for Creatinine Clearance: Refrigeration Requirements
Yes, 24-hour urine samples for creatinine clearance should be refrigerated during collection to maintain sample integrity and ensure accurate results. 1
Storage Requirements During Collection
- Samples should be refrigerated for assay the same or next day, as recommended by the American Journal of Kidney Diseases 1
- One freeze is acceptable if necessary, but repeated freeze-thaw cycles should be avoided 1
- Research demonstrates that urine creatinine is remarkably stable even under suboptimal conditions, with less than 3% decrease when stored for 2 days at 55°C 2
- However, refrigeration remains the standard practice to prevent bacterial growth and maintain overall sample quality 1
Additional Collection Guidelines
Pre-Collection Instructions
- Patients should refrain from vigorous exercise for 24 hours before sample collection, as physical activity can transiently elevate urinary creatinine excretion 1
Collection Technique
- The bladder should be emptied and urine discarded at the start of the collection period 3
- At the end of the 24-hour period, the patient should empty the bladder just before the interval ends, and this final void is included in the collection 3
- Three or more bladder voidings are generally necessary for accurate urine collections 3
Alternative Collection Durations
- For patients who void infrequently (fewer than 3 times in 24 hours), a 48-hour collection should be performed to avoid sampling errors 3
- For polyuric patients or children, a supervised 12-hour collection may be sufficient if they void frequently enough 3
- The longer the collection interval, the more reliable the results, assuming patient compliance 3
Common Pitfalls to Avoid
- Incomplete 24-hour collections are the most common source of error when measuring creatinine clearance 1
- Failure to refrigerate samples may lead to bacterial overgrowth, though creatinine itself remains relatively stable 2
- Missing the final void or including urine from before the collection start time will significantly affect accuracy 3