To properly preserve urine samples for interleukin measurement, follow these key steps based on laboratory best practices:

Immediate Handling: Collect urine in sterile, endotoxin-free containers. Centrifuge at 1,500–3,000 × g for 5–10 minutes within 1 hour of collection to remove cellular debris and particulates.

Storage Temperature:

For short-term storage (≤72 hours), keep samples at 2–8°C.

For long-term storage (>72 hours), aliquot the supernatant (avoid repeated freeze-thaw cycles) and store at -80°C. This minimizes protein degradation, which is critical for preserving interleukins (heat-labile cytokines).

Additives (if needed): In some cases, adding protease inhibitors (e.g., phenylmethylsulfonyl fluoride, PMSF) or sodium azide (0.05–0.1% final concentration) can prevent enzymatic breakdown of interleukins. Confirm compatibility with your ELISA kit, as some additives may interfere with antibody binding.

Thawing: When ready for use, thaw frozen samples slowly on ice. Mix gently (avoid vortexing) and centrifuge again briefly to remove any precipitates before assaying.

These steps help maintain interleukin stability, ensuring reliable results in ELISA measurements. Always refer to your specific ELISA kit instructions for any protocol adjustments.