Stability of salivary cortisol, alpha-amylase, and chromogranin A after long-term storage

The presence of stress biomarkers in saliva provides a convenient target to study body response in various conditions as well as in biobanking research. However, there are many conditions that may affect the assessment of these markers. Currently, there is no consensus over how long the saliva can be stored where the values of these markers remain stable. This study aims to investigate whether storage duration affects the measured concentrations of salivary cortisol (sCort), alpha-amylase (sAA), and chromogranin A (sCgA). Saliva samples were measured for sCort levels using an enzyme immunoassay kit, for sAA activity using a portable biosensor, and for sCgA levels using an ELISA kit soon after collection. Remeasurement was performed after storage at -80 °C for 3, 3.5, and 4 years (n = 15, 10, 15, respectively). The remeasured values of sCort and sAA were not different from the original measurement at all time points (p = 0.221 and p = 0.861, respectively). Surprisingly, the remeasured values of sCgA significantly increased compared with the original measurement (p < 0.000). No significant changes were observed for sCort and sAA values after up to 4 years of storage while long-term storage of sCgA is not recommended as values would greatly differ from immediate measurement.