Evaluating storage conditions for insulin and parathyroid hormone testing

Objectives: The objective of the study is to evaluate the stability of insulin and parathyroid hormone (PTH) under various storage conditions and blood collection tube types and to assess the effects of time and temperature on hormone degradation. Materials and Methods: Blood samples were collected in three types of tubes: Serum separator, ethylenediaminetetraacetic acid plasma, and heparin plasma. Aliquots were stored at room temperature, 4°C, and −20°C. Hormone concentrations of insulin (μIU/mL) and PTH (pg/mL) were measured at 0, 1, 6, and 24 hours at room temperature and 4°C, and at 24, 48, and 72 hours at −20°C using immunoassays. The impact of storage duration and freeze-thaw cycles was observed. Data were plotted to compare degradation trends and variability across conditions. Statistical analysis: Descriptive statistics (mean, standard deviation) were used to represent biological replicates. No inferential statistics were applied, as the study was exploratory in nature. Results: Both insulin and PTH exhibited rapid degradation at room temperature, particularly within the first 24 hours. Hormone stability was better at 4°C and best preserved at −20°C, with minimal degradation up to 72 hours. Among the tube types, serum separator tubes provided superior stability, especially at room temperature. Variability in hormone concentrations was lowest under frozen conditions and highest at room temperature. Conclusions: Cold storage, particularly at −20°C, is essential for maintaining the stability of insulin and PTH in clinical and research samples. Serum separator tubes showed favorable stability characteristics when processing was delayed.