Abstract Background Routine urinalysis is performed to aid in the diagnosis and monitoring of metabolic disorders, urinary tract infections and kidney and liver function abnormalities. According to the Clinical and Laboratory Standards Institute (CLSI) guidelines, urinalysis should be performed within two hours of urine collection. If a delay is inevitable, the samples must be preserved either by refrigeration (4-8°C) or stored using preservatives. Due to ongoing consolidation in many laboratories, samples spend several hours in transit before testing at a centralized laboratory necessitating the need for refrigerated transport (4-8°C) or preservation using preservatives (and transport at room temperature). In our laboratory, all urinalysis specimens are refrigerated after collection and 99% of specimens are tested with 24 hours of collection. The remaining 1% require preservation. Some commonly used urine preservatives for urinalysis include the Stabulir tablets and the mercury free urinalysis preservative tubes, such as the BD Vacutainer Plus Conical UA Preservative tubes. CLSI recommends that, prior to implementation in the laboratory, commercially available urine preservation systems must first be evaluated to confirm their fit for purpose. The aim of the study is to evaluate the stability of urine specimens for urinalysis in the BD Vacutainer Plus Conical UA Preservative Tubes. Methods Thirty (30) urine specimens partitioned into 4 aliquots were analyzed at different time points in this study. Urine was collected in 90 mL sterile orange cap urinalysis containers and transported to the laboratory at 4-8°C. In the laboratory, the samples were gently mixed and partitioned into 4 aliquots; aliquots 1 (neat) were analyzed routinely within 24 hours of collection and patient results reported (reference result). Aliquots 2, 3 and 4 were transferred into BD Vacutainer Plus Conical UA preservative tubes, gently mixed according to manufacturer’s instructions and kept at room temperature. Aliquots 2 were analyzed within 24 hours of collection (same time with neat samples) and resulted as reference preservative results (day 0). Aliquots 3 and 4 were analyzed at 24 and 48 hours, respectively, for chemical urinalysis and microscopy. Samples were analyzed on the Siemens Atellica® 1500 automated urinalysis and Atellica® UAS 800 Urine Sediment Analyzers. The acceptance criteria used were +/- 1 Pad (category) difference between test and reference results, and agreement /= 90%. Data was analyzed using Microsoft Excel. Results All analytes (glucose, hemoglobin, ketones, leucocytes, nitrite, protein and specific gravity) were stable for 48 hours (agreement /= 90 %) in preservative tubes except for appearance (clear, cloudy or turbid) with 89.1% agreement with reference results. For microscopic and particles analysis, all other parameters were stable for 48 hours when compared to the original reported result (agreement /= 90%) except for crystal types (88.9% agreement). Conclusion Urine for urinalysis is stable (within +/- 1 Pad difference) for up to 48 hours in the BD Preservative tube based on an acceptance criterion of /= 90% agreement between reported results and samples in preservative tubes. Apart from appearance and crystal type, all other parameters showed acceptable stability for up to 48 hours in the urine preservative tubes.
Agbor et al. (Wed,) studied this question.