Evaluation of resting cortisol concentration testing in dogs with chronic gastrointestinal signs

Background Resting cortisol concentrations are routinely measured in dogs with chronic gastrointestinal signs to rule out hypoadrenocorticism based on a concentration >2 mu g/dL (>55 nmol/L). Hypothesis/Objectives To assess the cross-sectional prevalence of hypoadrenocorticism in a group of dogs with chronic gastrointestinal signs presented to a referral internal medicine service. Animals Two-hundred and eighty-two client-owned dogs with chronic gastrointestinal signs and with resting cortisol concentration testing performed. Methods Retrospective review of medical records (final diagnosis, resting cortisol concentration, and adenocorticotropic hormone [ACTH] stimulation test results) of a referral population of dogs between May 2013 and September 2017. Results Resting cortisol concentration was <2 mu g/dL (<55 nmol/L) in 79 patients (28%). Repeated resting cortisol concentration measurements were performed in 28 dogs, and in 8, resting cortisol concentrations remained <2 mu g/dL (<55 nmol/L). Post-ACTH cortisol concentration was <2 mu g/dL (<55 nmol/L) in 1 dog, consistent with a diagnosis of hypoadrenocorticism and giving a prevalence estimate of hypoadrenocorticism in this population of dogs of 0.3% (95% confidence interval [95CI], 0.03-1.5%). In 19 dogs with an initial resting cortisol concentration <2 mu g/dL (<55 nmol/L), hypoadrenocorticism was excluded based on a repeat resting cortisol concentration >2 mu g/dL (>55 nmol/L). Overall, the most common diagnosis was chronic primary inflammatory enteropathy (176/282, 62.4%), followed by extragastrointestinal neoplasia (17/282, 6%), protein-losing enteropathy, pancreatitis and megaesophagus (10/282, 3.5% each). Conclusions and Clinical Importance Although dogs with hypoadrenocorticism can present with chronic gastrointestinal signs, it was the final diagnosis in only 1 of 282 dogs presenting to a referral internal medicine service for signs of chronic enteropathy. Repeated resting cortisol concentration may be considered as a test to try and exclude hypoadrenocorticism.