The effect of storage conditions on salivary cortisol concentrations using an Enzyme Immunoassay

Abstract

Saliva samples are easy to collect and are applicable for home-sampling, e.g. when studying HPA-axis dynamics to characterize diurnal cortisol profiles and the cortisol awakening response. However, the storing and transport conditions might be critical in the home-sampling approach. Here, we tested the stability of saliva cortisol in samples stored at different temperatures and after repeated thawing-freezing cycles when measured with an Enzyme Immuno Assay (EIA). Thirteen healthy volunteers, six women and seven men, mean age 31 (range 26–49) years collected saliva either in the morning hours (08:00–10:00 h) or before lunch (11:00–12:00 h). Storage at six different conditions were tested: Storage at − 18°C, − 4°C, 4°C and room temperature for 72 h. One condition tested was at − 18°C for 72 h and then kept in an envelope for 72 h with a freezing element in room temperature surroundings where after it was stored at − 80°C. The last tube was stored directly at − 80°C and served as the ‘gold standard’. The saliva samples were assayed using Salivary Cortisol Diagnostic EIA. Differences in cortisol measurements between each of the five conditions and the ‘gold standard’ (− 80°C) were evaluated by one-sample t-test. No significant differences were observed. This indicates that an EIA method can be used reliably when measuring salivary cortisol samples obtained by home-sampling including a postal delivery.

Key Words::

• Cortisol
• Enzyme Immuno Assay
• HPA-axis
• saliva
• storage
• stability

Acknowledgements

We thank Anetta Claussen and Mette Søgaard Hansen for their skilled assistance in the laboratory. We thank Anders Bue Marcussen for methodological discussions, William Frank Hurst for methodological instructions and Amarnadh Nalla for statistical support. The Dagmar Marshalls Foundation, Danish Medical Research Council, The Health Science Faculty, University of Copenhagen, and the Lundbeck Foundation are thanked for financial support.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.