Study sharpens cortisol testing strategy for suspected Addison’s

A newly published study in the Journal of Veterinary Internal Medicine takes a fresh look at one of small animal internal medicine’s most familiar endocrine dilemmas: how to interpret basal cortisol and ACTH stimulation testing in dogs being worked up for hypoadrenocorticism. Drawing on 982 dogs, the paper examines not just screening performance, but also how prior glucocorticoid exposure and additional hormone data can change the meaning of a low cortisol result in practice. (academic.oup.com)

That question matters because the field has long relied on a two-step framework. Basal cortisol is widely used as a screening tool, largely because a value above 2 µg/dL makes hypoadrenocorticism unlikely in most untreated dogs. But the tradeoff has always been specificity: many dogs with low basal cortisol do not have Addison’s, which is why AAHA guidance and diagnostic laboratory recommendations still say that low resting cortisol should be followed by an ACTH stimulation test rather than treated as diagnostic on its own. (meridian.allenpress.com)

Earlier studies helped define those tradeoffs. A 2007 JAVMA study found that basal cortisol concentrations of 2 µg/dL or less were highly sensitive, but much less specific, whereas a lower 1 µg/dL threshold improved specificity substantially. A larger 2016 JVIM analysis likewise found that 2 µg/dL was useful for ruling disease out, while a lower cutoff around 0.8 µg/dL improved the balance between sensitivity and specificity, though at the cost of missing some affected dogs. (pubmed.ncbi.nlm.nih.gov)

The new 982-dog paper builds on that literature with a larger contemporary dataset and a more clinically messy population, including dogs with recent glucocorticoid exposure. According to the article record, the investigators also examined dogs without hypoadrenocorticism that nevertheless had “flat-line” ACTH stimulation test results, and used aldosterone and endogenous ACTH data in at least some cases to sort out whether those results reflected true adrenal disease or suppression related to prior steroid treatment. That’s an important distinction, because exogenous glucocorticoids can suppress the hypothalamic-pituitary-adrenal axis and produce low pre- and post-ACTH cortisol values that mimic hypoadrenocorticism. (academic.oup.com)

Expert guidance has been pointing in that direction for some time. Michigan State University’s Veterinary Diagnostic Laboratory notes that recent glucocorticoid treatment can make ACTH stimulation results difficult to interpret, and that aldosterone testing may help when cortisol findings are confounded. A recent review on diagnosis of canine spontaneous hypoadrenocorticism similarly notes that basal cortisol is best used as a screening test, not a confirmatory one, and that endogenous ACTH and aldosterone testing can help distinguish primary disease, central disease, and isolated glucocorticoid deficiency in selected cases. (cvm.msu.edu)

Why it matters: For general practitioners, emergency clinicians, and internists, this is less about replacing the ACTH stimulation test than about using each test more intelligently. A dog with compatible signs and a basal cortisol above 2 µg/dL can often be moved away from an Addison’s diagnosis, saving time and cost for the pet parent. But a low basal cortisol still opens a broad differential, not a conclusion. The study’s focus on prior steroid exposure is especially relevant in referral and emergency settings, where dexamethasone, prednisone, topical steroids, or ear medications may already be in the picture before endocrine testing is pursued. (meridian.allenpress.com)

The deeper clinical takeaway may be about avoiding overdiagnosis as much as catching true disease. If more dogs without hypoadrenocorticism can show very low cortisol responses after glucocorticoid exposure, then medication history, sample timing, and selective use of aldosterone or endogenous ACTH become more important parts of the diagnostic algorithm. That could be particularly useful in dogs with normal sodium and potassium concentrations, where “atypical” or glucocorticoid-deficient presentations already complicate interpretation. (academic.oup.com)

What to watch: The next question is whether this paper changes frontline recommendations from specialty groups, reference labs, or teaching hospitals, especially around cortisol cutoffs and workup of dogs tested after recent glucocorticoid exposure. It may also spur more interest in adjunctive testing, including aldosterone and endogenous ACTH, for equivocal cases where a standard ACTH stimulation result doesn’t cleanly answer the question. (academic.oup.com)