Long-term stability of salivary cortisol

Area of Science:

• Endocrinology
• Biochemistry
• Clinical Chemistry

Background:

• Salivary cortisol measurement is a non-invasive method for assessing hypothalamic-pituitary-adrenal axis activity.
• Research often necessitates long-term storage of saliva samples due to project protocols or funding limitations.
• Understanding the impact of storage conditions on cortisol stability is crucial for reliable research findings.

Purpose of the Study:

• To investigate the effects of prolonged storage at various temperatures on salivary cortisol concentrations.
• To determine the stability of cortisol in saliva samples stored under different conditions.
• To provide recommendations for optimal long-term storage of salivary cortisol samples for research.

Main Methods:

• Saliva samples were collected from five subjects using polyester Salivette tampons.
• Samples were stored at 5°C, -20°C, -80°C, and room temperature for varying durations.
• Cortisol analysis was performed using Spectria RIA kits, with storage effects evaluated using a linear regression model.

Main Results:

• No significant decrease in cortisol concentrations was observed after storage at 5°C for up to 3 months or at -20°C/-80°C for up to one year.
• Cortisol concentrations decreased by 9.2% per month when stored at room temperature.
• Repeated freeze-thaw cycles (up to four times) did not affect measured cortisol levels.
• Samples stored on tampons showed higher variability (CVresid) compared to those stored in vials post-centrifugation.

Conclusions:

• Centrifuged saliva samples for cortisol analysis can be reliably stored at 5°C for up to 3 months or at -20°C/-80°C for at least one year.
• Long-term storage of salivary cortisol samples at room temperature is not recommended due to significant degradation.
• The stability of cortisol is not compromised by repeated freezing and thawing, suggesting flexibility in sample handling.