For urine samples, which long-term storage condition is recommended?

The recommended long-term storage condition for urine samples is frozen storage. Freezing urine samples preserves the integrity of the chemical compounds, metabolites, and potential biological markers contained within the specimen. When urine is frozen, enzymatic activity and microbial growth are significantly slowed or halted, which helps to maintain the sample's viability for analysis over prolonged periods.

Storing urine samples at room temperature or in the refrigerator can lead to degradation of certain substances due to the continued metabolic activity of bacteria or other organisms. This can affect the reliability of test results and potentially compromise the sample’s usefulness for forensic analysis.

In contrast, other storage methods, such as drying or temperature-controlled storage that does not involve freezing, do not effectively prevent breakdown processes for many compounds found in urine. Therefore, freezing is the most reliable method for ensuring that urine samples remain intact and that the information they contain is preserved for future analysis.