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

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. 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. 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. 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.