Low‐dose ACTH stimulation testing in dogs suspected of hypoadrenocorticism

BACKGROUND: Low‐dose ACTH stimulation testing would lower cost and may increase sensitivity for identification of partial ACTH deficiency. HYPOTHESIS: (1) The low‐dose ACTH stimulation test will provide comparable results to the standard‐dose ACTH stimulation test in dogs suspected of hypoadrenocorticism and (2) partial ACTH deficiency exists in dogs and can result in chronic, intermittent gastrointestinal signs. ANIMALS: Thirty‐one client‐owned dogs suspected of having hypoadrenocorticism. METHODS: Prospective study. Dogs suspected of having hypoadrenocorticism received 1 μg/kg cosyntropin IV for the first ACTH stimulation test; the second test was performed 4 h later and dogs received 5 μg/kg cosyntropin IV. Blood samples were obtained pre‐ACTH and 1 hour post‐ACTH for each dose (4 measurements total). Samples for endogenous ACTH measurement were obtained at the time of initial blood collection. RESULTS: No significant difference was observed in the basal cortisol concentration before administration of a 1 μg/kg versus before a 5 μg/kg dose of cosyntropin (P = .544). For dogs suspected of having hypoadrenocorticism, the ACTH‐stimulated cortisol concentrations in response to both doses of ACTH were equivalent (90% confidence interval [CI], 80.5‐97.2%; P = .04). No cases with partial ACTH deficiency were identified conclusively. CONCLUSIONS AND CLINICAL IMPORTANCE: A 1 μg/kg dose of cosyntropin is equivalent to a 5 μg/kg dose of cosyntropin for screening dogs suspected of hypoadrenocorticism. The existence of partial ACTH deficiency was not identified in this small group of dogs.