OBJECTIVES: Stability of concentrations of urinary stone-related metabolites was analyzed from samples of recurrent urinary stone formers to assess necessity and effectiveness of urine acidification during collection and storage. METHODS: First-morning urine was collected from 20 adult calcium-stone forming patients at Tomas Bata Hospital in the Czech Republic. Urine samples were analyzed for calcium, magnesium, inorganic phosphate, uric acid, sodium, potassium, chloride, citrate, oxalate, and urine particles. The single-voided specimens were collected without acidification, after which they were divided into three groups for storage: samples without acidification ("NON"), acidification before storage ("PRE"), or acidification after storage ("POST"). The analyses were conducted on the day of arrival (day 0, "baseline"), or after storage for 2 or 7 days at room temperature. The maximum permissible difference (MPD) was defined as ±20 % from the baseline. RESULTS: The urine concentrations of all stone-related metabolites remained within the 20 % MPD limits in NON and POST samples after 2 days, except for calcium in NON sample of one patient, and oxalate of three patients and citrate of one patient in POST samples. In PRE samples, stability failed in urine samples for oxalate of three patients, and for uric acid of four patients after 2 days. Failures in stability often correlated with high baseline concentrations of those metabolites in urine. CONCLUSIONS: Detailed procedures are needed to collect urine specimens for analysis of urinary stone-related metabolites, considering both patient safety and stability of those metabolites. We recommend specific preservation steps.

Birmingham Quality University Hospitals NHS Foundation Trust Birmingham UK

Clinical Department of Laboratory Medicine University Hospitals Leuven Leuven Belgium

Clinical Pathology Laboratory Department of Medical Biochemistry and Hacettepe University Hospitals Hacettepe University Faculty of Medicine Ankara Türkiye

College of Education Salzburg Austria

Department of Clinical Biochemistry and Pharmacology 37742 Tomas Bata Hospital Zlín Zlín Czech Republic

Department of Clinical Chemistry University of Helsinki Espoo Finland

Department of Laboratory Medicine Paracelsus Medical University Salzburg Austria

Hospital District of Helsinki and Uusimaa HUS Diagnostic Center HUSLAB Helsinki Finland

Institute of Clinical Biochemistry and Diagnostics Medical Faculty in Hradec Králové Charles University Prague Czech Republic

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