Variable Control and Its Influence Before Urine Sample Analysis in a Field Environment.

Background and Objectives: The aim of the study was to store urine samples at different temperatures and humidity levels and analyze common biochemical test results and point-of-care testing (POCT) indicators according to different storage times and evaluate whether the samples should be centrifuged to study the best storage conditions for urine samples. Methods: Random midstream urine samples (100 mL) were collected from 10 healthy individuals. A portion of the samples was centrifuged. The remaining samples were not centrifuged and were stored under different temperature and humidity conditions for different periods. We measured urine indicators ([Na+], [K+], [Cl-], gamma-glutamyl transpeptidase [GGT], urea, and creatinine [Cr]) at 2, 4, 24, and 72 hours and 7 and 55 days, and we used POCT to measure myoglobin (Mb) and microalbumin (mAlb) concentrations. Results: Centrifugation of urine samples decreased the measured GGT and increased the measured Mb. In urine samples stored at 4°C and room temperature, electrolyte concentrations were scarcely affected by storage time. After storage at 50°C for 24 hours, the measured [Na⁺] and [Cl^-] levels changed. Metabolites (urea and Cr) underwent no obvious change across temperatures. GGT did not change during long-term storage at 4°C. The mAlb level changed significantly only after storage at 4°C. When stored at 4°C, Mb changed little within 4 hours. Under humid conditions, [Na⁺] and [Cl^-] increased significantly after 24 hours, and urea decreased significantly after 7 days of storage. Under dry storage conditions, urinary Cr and GGT decreased, and under humid conditions, these concentrations increased. At high humidity, mAlb increased significantly after 72 hours. Conclusions: Electrolyte and amino acid metabolite concentrations were less affected by storage time at 4°C and room temperature than at other temperatures. Some proteins are sensitive to environmental changes; samples collected for quantification of these proteins can be stored briefly at 4°C after centrifugation. Normal humidity conditions meet most physiological testing requirements.