The short-term reliability and long-term stability of salivary immune markers.

Salivary markers of immune function are increasingly commonly used in studies of human health. Yet, few studies have examined the short-term or long-term reliability or stability of these biomarkers, making their measurement properties unclear. We addressed this issue in the present study by collecting two saliva samples, two hours apart, from 426 adolescent girls during a baseline laboratory visit. Then, eighteen months later, we collected the same samples again from a subset of these participants (n = 113). The correlations between the two samples collected at each session were generally high (mean r = 0.67). In contrast, although single saliva samples were only weakly correlated across 18 month (mean rs = 0.18), averaging the two quantifications within a session considerably improved the reliability (mean r = 0.27). In short, salivary immune markers exhibited strong short-term test-retest correlations, and averaging across multiple assessments notably improved long-term test-retest correlations. Additional research is needed to establish the health relevance and mechanisms underlying these potentially useful, non-invasive biomarkers.