Effects of concentration of Na₂CO₃-containing stabilizer on urinary C-peptide examination

Abstract

Urinary C-peptide examination is used as an indirect method of assessing the level of insulin production. We use 24-h urine samples as materials for examination. We use a Na₂CO₃-containing stabilizer of urinary C-peptide. Under acidic conditions, C-peptide is unstable and is decomposed by growing bacteria. However, the effect of the concentration of the Na₂CO₃-containing stabilizer on the measurements of collected urine volume is unknown. We examined the effects of the concentration of the Na₂CO₃-containing stabilizer, storage temperature, and bacterial presence on the measurements of collected urine volume. According to our results, CPR was decomposed by growing bacteria, and the urinary CPR concentration decreased when the collected urine volume per package of the stabilizer exceeded 4,000 mL at room temperature. When we chilled and preserved urine with low concentrations of the stabilizer, CPR was stable. In addition, in the case of the collected urine volume that was less than 300 mL per package of the stabilizer, the urine CPR concentration decreased. After examining the effects of both pH and salt concentration, we considered that salt concentration has a greater effect than pH on CPR when a high concentration of the stabilizer is used. Therefore, we must determine the appropriate concentration of the Na₂CO₃-containing stabilizer for a particular collected urine volume before measurements.