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 ≤ 1 μg/dL or ≤ 2 μg/dL to detect dogs with hypoadrenocorticism were estimated by use of the ACTH stimulation test as the gold standard.
Results—Basal cortisol concentrations of ≤ 1 μg/dL had excellent sensitivity (100%) and specificity (98.2%) for detecting dogs with hypoadrenocorticism. For basal cortisol concentrations of ≤ 2 μg/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 μg/dL that are not receiving corticosteroids, mitotane, or ketoconazole are highly unlikely to have hypoadrenocorticism. However, if the basal cortisol concentration is ≤ 2 μg/dL, little to no information regarding adrenal gland function can be obtained and an ACTH stimulation test should be performed.