Basal Serum Cortisol Concentration as a Screening Test for Hypoadrenocorticism in Dogs

Abstract

BackgroundMeasurement of basal serum or plasma cortisol concentration is used as a screening test for hypoadrenocorticism in dogs, but is not well characterized.ObjectivesTo evaluate the sensitivity and specificity of basal serum cortisol to detect hypoadrenocorticism in a population of dogs with a clinical suspicion of hypoadrenocorticism.AnimalsFour hundred and fifty dogs with nonadrenal gland illness and 14 dogs with naturally occurring hypoadrenocorticism were included.MethodsRetrospective case‐control study. The records of all dogs having had an ACTH stimulation test performed between January 2005 and September 2011 at the University of Bristol were reviewed. Dogs were included if the test was performed as a screening for hypoadrenocorticism. The sensitivity and specificity of basal serum cortisol concentration to detect dogs with hypoadrenocorticism were calculated using 2 cut‐offs and compared to the gold standard ACTH stimulation test.ResultsUsing a cut‐off of ≤2 μg/dL (≤55 nmol/L), the sensitivity and specificity of basal cortisol to detect hypoadrenocorticism were 100% and 63.3%, respectively, whereas for a cut‐off of ≤1 μg/dL (≤28 nmol/L), the sensitivity and specificity were 85.7% and 91.8%, respectively.Conclusions and Clinical ImportanceMeasurement of basal serum cortisol is useful as a screening test for hypoadrenocorticism in dogs using a cut‐off of ≤2 μg/dL (≤55 nmol/L), and the disease is unlikely with a basal serum cortisol >2 μg/dL (>55 nmol/L). A basal serum cortisol ≤2 μg/dL (≤55 nmol/L) cannot be used to diagnose hypoadrenocorticism, and an ACTH stimulation test should be performed in these cases.

Evaluation of the Cortisol‐to‐ACTHRatio in Dogs with Hypoadrenocorticism, Dogs with Diseases Mimicking Hypoadrenocorticism and in Healthy Dogs

“…Determination of baseline serum cortisol concentration has a high sensitivity (100% if >2 μg/dL) to exclude HA, but a low specificity of only 63.3–78.2% 9, 10. In our study, although having the same sensitivity of 100%, its specificity was only 20%.…”

“…This situation has prompted a need for alternative tests with which to diagnose HA. Measurement of baseline cortisol concentration has been shown to be a useful screening test to rule out HA 9, 10. The disease is unlikely with a baseline serum cortisol >2 μg/dL (>55 nmol/L) 9, 10.…”

“…The disease is unlikely with a baseline serum cortisol >2 μg/dL (>55 nmol/L) 9, 10. However, due to that test's rather low specificity, an ACTH stimulation test must be performed in dogs with a baseline cortisol ≤2 μg/dL to safely exclude HA 9, 10…”

Hydrocortisone in the management of acute hypoadrenocorticism in dogs: a retrospective series of 30 cases

“…, Bovens et al . ). However, values below this cut‐off are not specific for hypoadrenocorticism, and the lack of cortisol stimulation following ACTH administration provides more substantive evidence of hypoadrenocorticism.…”

“…The most commonly reported intravenous dosages of dexamethasone for hypoadrenocorticism include 0·2 to 0·5 mg/kg once (Plumb ); 0·1 to 2·0 mg/kg followed by 0·05 to 0·1 mg/kg every 12 hours (Scott‐Moncrieff ), 0·5 to 2 mg/kg followed by 0·05 to 0·1 mg/kg every 12 hours (Bovens et al . ) and 2 to 4 mg/kg every 2 to 6 hours (Kintzer & Peterson ). This equates to a dose of 2·67 mg/kg hydrocortisone at the lowest recommended dexamethasone dose (0·1 mg/kg for 12 hours) or 107 mg/kg at the highest dose (4 mg/kg every 2 hours) compared with maximum respective hydrocortisone doses used in this study of 7·5 mg/kg and 1·25 mg/kg over a similar time period (12 and 2 hours, respectively).…”