Impact of chemical preservative in urine samples

Urinalysis is one of the most important tests in the clinical laboratory. In this study we assessed the use of chemical preservative in urinalysis during preanalytical phase. Fifty first morning urine samples from medical laboratory patients were collected and stored with and without chemical preservative. Difference between medians were analyzed using Wilcoxon signed rank test for glucose, bilirubin, ketones, specific gravity, erythrocytes, pH, proteins, nitrites, leukocytes using urine strips; and on leukocytes, erythrocytes, epithelial cells, and bacteria in the urinary sediment, at 90 minutes after sampling. Our results showed that the specific gravity and the pH values increased in samples with chemical preservative in urine strip tests. Concerning urinary sediment analysis no differences were observed in the studied parameters between samples with and without chemical preservative. We suggest that the effect on urine pH is due to the chemical nature of the substances in the preservative. Thus, we caution about the use of chemical preservatives in samples to be analyzed within short time (i.e. less than 1.5 - 2 hours) after sample collection. Avoid chemical preservatives, in this situation, could help avoid changes in the pH and specific gravity, which could eventually help in maintaining quality in the preanalytical phase of urinalysis.