Feasibility and usefulness of in-hospital and at-home salivary sampling in healthy dogs and trilostane-treated dogs with Cushing's syndrome: a prospective observational study

Background: Monitoring Cushing's syndrome (CS) in dogs remains a significant challenge and currently relies on clinical signs, biochemistry results and hormone tests, such as prepill or post-ACTH cortisol. Salivary cortisol testing at home, effective in humans, could benefit dogs by minimizing in-hospital fear impacts on cortisol measurements. The objectives of this study were to (1) assess the feasibility of saliva sampling in client-owned dogs and (2) compare at-home and in-hospital salivary cortisol concentrations for monitoring trilostane treatment. Ten healthy controls and 38 trilostane-treated dogs with CS were included in this prospective observational clinical trial. Saliva was collected using a ginger-dipped Salimetrics swab held in the dogs' mouths for 30 seconds. Saliva was collected from controls at the hospital and at home. For trilostane-treated dogs, saliva was collected in the hospital before blood sampling for prepill serum cortisol and at home by owners. Salivary cortisol concentrations were measured using liquid chromatography high-resolution mass spectrometry (LC-HRMS), and serum cortisol by LC-HRMS and chemiluminescence immunoassay. Dogs with CS were classified as well-controlled if clinical signs had resolved. Results: In-hospital and at-home saliva sampling was successful in all 10 controls, but only in 18/38 (47%) and 7/18 (39%) dogs with CS, respectively. Salivary cortisol was significantly lower at home in CS dogs but not in controls. Among the 7 CS dogs sampled at both locations, the uncontrolled dog had the highest at-home cortisol level. Four of 6 well-controlled dogs had prepill serum cortisol above the target range, with at-home salivary cortisol undetectable in 3 and lower than the uncontrolled dog in one. Conclusion: Saliva sampling remains challenging in CS dogs. This method needs further refinement before stress-free, at-home salivary cortisol evaluation surpasses current monitoring techniques, such as prepill serum cortisol measurement. Registry: animex-ch, TRN: ZH076/19 and ZH153/22, Registration dates: 27 Juli 2019 and 22 September 2022.