Resting cortisol concentrations in dogs presenting to a university teaching hospital with collapse

Background: The relationship between collapse and a diagnosis of hypoadrenocorti-cism is not well understood in dogs.Hypothesis: To assess the prevalence of episodes of collapse in dogs screened forhypoadrenocorticism, and to assess the prevalence of confirmed hypoadrenocorti-cism in dogs presenting with reported collapse.Animals: Seventy-three client-owned dogs with resting cortisol concentrations weremeasured and presented to a University teaching hospital for collapse.Methods: Retrospective review of medical records of dogs at a single center.Results: The prevalence of episodes of collapse in dogs that had a resting cortisol mea-surement was 73/856 (8.5%; 95% confidence interval [95% CI], 6.7%-10.6%). Restingcortisol concentration was <2 μg/dL (<55 nmol/L) in 19 dogs. Cortisol concentration afterACTH stimulation was <2 μg/dL (<55 nmol/L) in 1 of the 73 dogs in this cohort, consis-tent with a diagnosis of hypoadrenocorticism, giving a prevalence estimate of hypoadre-nocorticism of 1.3% (95% CI, 0.15%-6.2%). In 8 dogs with an initial resting cortisolconcentration <2 μg/dL (<55 nmol/L), hypoadrenocorticism was excluded based on arepeat resting cortisol concentration >2 μg/dL (>55 nmol/L). The most common diagnosiswas vasovagal syncope (10/73), followed by sick sinus syndrome and third-degree atrio-ventricular block (2/73). The final diagnosis was unknown in 24/73 dogs.Conclusions and Clinical Importance: Hypoadrenocorticism was the final diagnosis in1 of 73 dogs presented to a teaching hospital either in a collapsed state or with a pre-vious history of episodes of collapse. No dog presenting as cardiovascularly stable forintermittent collapse was found to have hypoadrenocorticism.