Frozen saliva samples are often used for later determination of salivary glucocorticoids in research studies on stress and endocrine disorders. We studied the stability of cortisol and cortisone in saliva after six years of storage at -80 °C by repeated analysis of 153 stored aliquots, collected with Salivette®, using liquid chromatography tandem mass spectrometry. We found a very high agreement between the first and the repeated measurement after six years at -80 °C, for both cortisol and cortisone concentrations (rs= 0.96 and rs= 0.98, respectively). Passing-Bablok regression equations were y = 0.02 + 1.00x and y = 0.02 + 1.14x for cortisol and cortisone, respectively. We conclude that salivary cortisol and cortisone concentrations remain essentially unaltered after six years of storage at -80 °C.
Keywords: Liquid chromatography; biobanking; long-term storage; mass spectrometry; pre-analytical phase; salivary cortisol; salivary cortisone; stability; ultra-low temperature.