Use of a Low‐Dose ACTH Stimulation Test for Diagnosis of Hypoadrenocorticism in Dogs

Abstract

Background: Although definitive diagnosis of hypoadrenocorticism usually is made by an adrenocorticotrophic hormone (ACTH) stimulation test using 250 mg/dog of synthetic ACTH (cosyntropin/tetracosactrin), increased costs have prompted a search for less-expensive diagnostic methods.Hypothesis: A low-dose ACTH stimulation test (5 mg/kg) will distinguish between dogs with nonadrenal illness and hypoadrenocorticism. Additionally, administration of cosyntropin will not affect the results of another ACTH stimulation test performed 24 hours later.Animals: Eight healthy adult dogs and 29 hospitalized dogs with suspected hypoadrenocorticism. Methods: In this prospective study, each healthy dog received 4 ACTH stimulation tests. Dogs received either 5 mg/kg or 250 mg/dog of cosyntropin on day 1 and the alternate dose on day 2. The opposite dosing sequence was used after a 2-week washout period (days 15 and 16). Dogs with suspected Addison's disease received 2 ACTH stimulation tests, 24 hours apart, using either a dose of 5 mg/kg cosyntropin or 250 mg/dog on the 1st day and the alternate dose on the 2nd day.Results: In healthy dogs, poststimulation cortisol concentrations on days 2 and 16 and days 1 and 15 were equivalent (90% confidence interval [CI]: 86.7-101.2%). In dogs with suspected Addison's disease, mean (AESD) cortisol responses to ACTH in the 5 mg/kg dose (16.2AE7.7 mg/dL) and 250 mg/dog dose (15.9AE6.3 mg/dL) were statistically equivalent (90% CI: 91.2-105.4%).Conclusions and Clinical Importance: Low-dose ACTH stimulation testing distinguishes between dogs with nonadrenal illness and hypoadrenocorticism. Additionally, the administration of 2 ACTH stimulation tests on consecutive days does not affect results of the second test.

A retrospective study of dogs with atypical hypoadrenocorticism: a diagnostic cut‐off or continuum?

“…This is a limitation of the study, because we cannot estimate with high accuracy what portion of the healthy dog population would be expected to have post-ACTH stimulation cortisol concentrations below the reference intervals provided by the laboratories. However, we identified several publications that used the Immulite® chemiluminescent assay (Siemen) in small numbers of healthy dogs (n≤20) and reported comparable ranges (Singh et al 1997, Cohn et al 2008, Lathan et al 2008, Ginel et al 2012). …”

Hypoadrenocorticism

“…Initial emergency treatment may need to be based on presence of characteristic clinical signs and electrolyte abnormalities; however the diagnosis should always be confirmed with an ACTH stimulation test prior to initiating long term treatment. dysfunction is 5 μg/kg (Lathan, 2008). Synthetic polypeptides containing the biologically active first 24 amino acids of ACTH (Cortrosyn [cosyntropin] or Synacthen [tetracosactrin]) are the products of choice for performing an ACTH stimulation test (Behrend, 2013).…”

“…Once treatment has been initiated, it is very difficult if not impossible to confirm the diagnosis without withdrawing treatment for several weeks. No differences in peak cortisol response between dosages of 5 μg/kg or 250 μg/dog have been documented in either healthy dogs or dogs with clinical signs of hypoadrenocorticism; therefore a dose of 5 μg/kg is recommended to decrease the cost of testing (Kerl, 1999;Frank et al, 2000;Behrend et al, 2006;Lathan et al, 2008;Fig. Not all of these products have been directly compared in dogs but they are considered interchangeable.…”

Comparison of 2 Doses for ACTH Stimulation Testing in Dogs Suspected of or Treated for Hyperadrenocorticism

“…As ACTH stimulation tests for dogs receiving trilostane must be initiated at a specific time post pill, both tests could not be performed in a single day. Accordingly, a test using a 1 μg/kg dose of cosyntropin IV was performed on day 1, and the second test (5 μg/kg cosyntropin IV) was performed the following day . All tests were initiated 4–6 hours post pill on day 1; for a particular dog, the second test was started at the same time post pill as on day 1.…”