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

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 hours 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 hours. These results were compared with those obtained from refrigerated, non-additive polystyrene (PS) tubes at 0, 4, and 8 hours. 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 hours, 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-hour 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 hours 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 hours of collection.