Lab Manager and Research Lead MySimplePetLab Denver, CO, United States
Abstract:
Background: Storage conditions may affect urine biochemical parameters. Urine samples in preservative-containing sample tubes may negate the effects of storage conditions.
Objective: To compare biochemical results and specific gravity (SG) for urine stored over 5 days in commercially available chlorhexidine preservative tubes and preservative-free (PF) plastic tubes.
Methods: For 8 pooled canine urine samples, we prepared 32 aliquots each (4 aliquots per sample set) for preservative tubes and PF tubes. Samples were analyzed immediately after adding urine to preservative and PF tubes; other aliquots were stored at room temperature and then designated aliquots were analyzed 3 and 5 days later. We used a urine strip reader and a refractometer.
Results: Bilirubin, blood, ketone, and leukocytes were unchanged or varied slightly over day, volume, and tube. Considering storage over time, the same 5/8 samples in PF tubes had both varying pH and 1-2-unit semi-quantitative differences in total protein (TP) but less variable urine protein-to-creatinine (UPC) ratios. Similarly, TP varied by 2 units for 4 samples in preservative tubes. Glucose varied in 3 samples in PF tubes and in 1 sample in preservative tube. Considering 1 vs 7mL urine volumes irrespective of day, 3-4 samples in preservative tubes had at least 2-unit differences for TP; UPC ratios varied slightly. Urine SGs were unaffected clinically.
Conclusion: Urine samples stored over 5 days at room temperature in tubes with and without chlorhexidine preservative yielded variable TP. The preservative tubes may not provide an advantage over PF tubes for urine biochemical parameters.
