Stability of urinalysis in two different preservative tubes: A comparative analysis

Abstract

Background

Sample stability represents a major challenge in the preanalytical phase of urinalysis. This study aimed to evaluate and compare the stability of urine samples stored at room temperature for up to 72 h in two commercially available chlorhexidine-based preservative tubes.

Methods

The study included 44 pathological urine samples. Urinalysis was performed after storage in BD Vacutainer® and Vacusera® tubes at 4, 8, 24, 48, and 72 h. These results were compared with those obtained from refrigerated, non-additive polystyrene (PS) tubes at 0, 4, and 8 h. A level of ≥90% agreement or a kappa value (κ) of ≥0.8 was deemed to represent perfect agreement and stability.

Results

Specific gravity, pH, glucose, bilirubin, urobilinogen and nitrite were stable in all tubes and conditions. Within the first 4 h, instability was detected in protein in the non-additive PS tube, in ketone and red blood cells (RBC) in the BD tube, and in white blood cells (WBC) in all tubes. By the 8-h mark, ketone and RBC in the non-additive PS tube, as well as bacteria count in the BD tube, failed to maintain stability. Notably, blood and leukocyte esterase remained stable for at least 8 h across all tubes.

Conclusions

Storage of urine samples in chlorhexidine-based preservative tubes has minimal impact on urinalysis; however, inter-manufacturer variability exists. To ensure reliable results, analysis should be performed within 4–8 h of collection.