Previous studies that included limited numbers of affected dogs have suggested basal cortisol concentrations ≤55 nmol/L (2 μg/dL) are sensitive, but nonspecific, for a diagnosis of hypoadrenocorticism. A detailed assessment of the diagnostic utility of basal cortisol concentrations is warranted.

The objective of the study was to evaluate the utility of basal cortisol concentrations for the diagnosis of hypoadrenocorticism in a large number of dogs, including those with and without serum electrolyte abnormalities. Five hundred and twenty-two dogs, including 163 dogs with hypoadrenocorticism, 351 dogs with nonadrenal gland illness, and 8 dogs with equivocal results were used in the study.

This was a retrospective study. Basal and post-ACTH cortisol concentrations and sodium and potassium concentrations were collected from medical records. A receiver operating characteristic (ROC) curve was constructed for basal cortisol concentrations by standard methodologies. Sensitivity, specificity, and predictive values were determined for various cut-points.

Results showed that the area under the ROC curve was 0.988 and was similarly excellent regardless of serum electrolyte concentrations. At the most discriminatory cut-point of 22 nmol/L (0.8 μg/dL), sensitivity and specificity were 96.9 and 95.7%, respectively. A basal cortisol concentration of ≤55 nmol/L (2 μg/dL) resulted in a sensitivity of 99.4%. Conversely, a basal cortisol concentration of ≤5.5 nmol/L (0.19 μg/dL) resulted in a specificity of 99.1%

In conclusion, similar to findings in previous studies, basal cortisol concentrations >55 nmol/L (2 μg/dL) are useful in excluding a diagnosis of hypoadrenocorticism. Interestingly, excellent specificities and positive predictive values were observed at lower cut-point cortisol concentrations.

Click here to be directed to the study in the Journal of Veterinary Internal Medicine.