Using basal cortisol levels to rule out Addison's disease in dogs

Abstract

OBJECTIVE: To determine whether basal serum or plasma cortisol concentration can be used as a screening test to rule out hypoadrenocorticism in dogs. DESIGN: Retrospective case-control study. ANIMALS: 110 dogs with nonadrenal gland illnesses and 13 dogs with hypoadrenocorticism. PROCEDURES: Sensitivity and specificity of basal serum or plasma cortisol concentrations of either <or= 1 microg/dL or <or= 2 microg/dL to detect dogs with hypoadrenocorticism were estimated by use of the ACTH stimulation test as the gold standard. RESULTS: Basal cortisol concentrations of <or= 1 microg/dL had excellent sensitivity (100%) and specificity (98.2%) for detecting dogs with hypoadrenocorticism. For basal cortisol concentrations of <or= 2 microg/dL, sensitivity was 100% but specificity was 78.2%. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of sensitivity and specificity, basal serum or plasma cortisol concentrations had high negative predictive values over a wide range of prevalence rates and can be used to rule out a diagnosis of hypoadrenocorticism. Dogs with basal cortisol concentrations > 2 microg/dL that are not receiving corticosteroids, mitotane, or ketoconazole are highly unlikely to have hypoadrenocorticism. However, if the basal cortisol concentration is <or= 2 microg/dL, little to no information regarding adrenal gland function can be obtained and an ACTH stimulation test should be performed.