Testing for Canine Hyperadrenocorticism

Diagnosis of hyperadrenocorticism (HAC) in dogs is based on clinical findings, adrenal function tests, and treatment response. However, the most common tests (ie, ACTH stimulation, low-dose dexamethasone suppression tests [LDDST]) are not always positive in dogs with HAC. Adrenal function testing may have cortisol concentrations consistent with HAC in dogs with nonadrenal disease and signs compatible with ACTH, resulting in misdiagnosis. Dogs with pituitary-dependent hyperadrenocorticism (PDH) and adrenal-dependent hyperadrenocorticism (ADH) often have increased plasma concentrations of noncortisol adrenal steroids, sometimes without increased plasma cortisol concentrations. Increases in noncortisol adrenal steroids may thus account for cases of HAC with negative adrenal function tests based on measurement of cortisol concentration.

A study was conducted to determine the role of plasma cortisol, androstenedione, estradiol, progesterone, testosterone, and 17-hydroxyprogesterone concentrations during ACTH stimulation testing of dogs with HAC signs. Significant differences were found for post-ACTH cortisol, post-ACTH progesterone, and post-ACTH 17-hydroxyprogesterone between dogs with or without HAC. Results supported the measurement of progesterone and 17-hydroxyprogesterone for HAC diagnosis in dogs with normal cortisol concentrations after ACTH administration but for which HAC is still suspected.

CommentaryMeasurement of post-ACTH noncortisol adrenal steroids may not provide a diagnostic advantage over post-ACTH cortisol for HAC diagnosis. This test, while sensitive, lacks specificity and should be used to rule out rather than diagnose HAC in dogs. However, because a majority of patients in this study were diagnosed with PDH, post-ACTH noncortisol adrenal steroids for diagnosis of ADH have not been thoroughly evaluated. In addition, studies evaluating adrenal steroidogenic enzyme activities in patients with adrenal and nonadrenal illness might provide insight into the utility of this test for diagnosis of canine HAC.—Jennifer Ginn DVM, MS, DACVIM

SourceConcentrations of noncortisol adrenal steroids in response to ACTH in dogs with adrenal-dependent hyperadrenocorticism, pituitary-dependent hyperadrenocorticism, and nonadrenal illness. Monroe WE, Panciera DL, Zimmerman KL. J VET INTERN MED 26:945-952, 2012.