04/14/2026
Scary disease for all of us veterinarians
Diagnosing Hypoadrenocorticism in Dogs: When to Suspect the Great Pretender
Hypoadrenocorticism (formerly known as Addison's disease) "the great pretender" because it mimics many other conditions, frequently with vague or intermittent signs that can confuse even the most experienced clinicians. If left untreated, this disease can have life-threatening consequences. But diagnosing this disease isn't impossible. With early diagnosis from a skilled veterinarian or a specialist, this condition can be treated and managed.
In this article, we'll discuss warning signs for both Hypoadrenocorticism with Electrolyte disturbances and eukalemic eukalemic Hypoadrenocorticism best diagnostic practices, and treatment methods to improve patient outcomes.
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What is Hypoadrenocorticism?
Clinical signs include:
Lethargy and weakness: Additionally, dogs with Hypoadrenocorticism may also be hesitant to exercise.
Gastrointestinal (GI) issues: This can include vomiting, diarrhoea, or weight loss, which may occur intermittently, adding to the challenge of diagnosis.
Polyuria and polydipsia (PU/PD): Electrolyte imbalances may result in impaired renal concentrating ability, leading to this condition.
Hypothermia: Acute cases can lead to a lower body temperature; clinically, this looks like lethargy, shaking, stiff muscles, and, in some cases, discoloration of gums.
Bradycardia Electrolyte imbalances as hyperkalemia create this low heart rate.
In severe cases, patients with these signs can present with a potentially life-threatening health crisis. Early diagnosis is essential for effective treatment and preventing these emergencies. However, identifying hypoadrenocorticism can be challenging because the clinical signs are often vague or nonspecific.
Hypoadrenocorticism with Electrolyte disturances and/or eukalemic, eunatremic Hypoadrenocorticism
Hypoadrenocorticism presents in two ways: with typical electrolyte chances or eukalemic eunatremic. Below, we'll differentiate between the two, offering insight as to why eukalemic euntremic hypoadrenocorticism can be more difficult to detect.
Identifying Primary Hypoadrenocorticism with Electrolyte disturbances
Primary Hypoadrenocorticism in canine patient frequently involves combined glucocorticoid and mineralocorticoid deficiency. On a chemistry panel, veterinarians will notice hyponatremia (low sodium levels), hyperkalemia (high potassium levels).
Identifying Eukalemic, Eunatremic Hypoadrenocorticism
In eukalemic, eunatremic hjypoadrenocorticism, electrolyte changes are absent, possibly due to isolated glucocorticoid deficiency. However, studies suggest that although many patients with eukalemic, eunatremic hypoadrenocorticism have minimal or absent aldosterone production, their sodium and potassium levels remain normal due to compensatory mechanisms, mainly in the kidney.
As a result, patients often have normal electrolyte levels, which makes diagnosis more challenging. The term "atypical Addisons" is today replaced by "eunatriemec, eulkaliemic hypoadrenocorticism," which typically presents with nonspecific clinical signs, like fatigue and gastrointestinal problems, that do not improve with standard treatments.
Due to these challenges, veterinarians should consider Hypoadrenocorticism as differential when patients present with the following clinical scenarios:
Non-responsive signs: Canine patients who present with persistent nonspecific signs, including vomiting, diarrhoea, lethargy, weight loss, or PU/PD, that don't respond to standard treatment.
Breed susceptibility: Some breeds are genetically predisposed to have Hypoadrenocorticism, including Standard Poodles, Rottweilers, and Great Danes.
Stress-related flare-ups: Intermittent clinical signs are a warning sign, but even more so when they intensify after periods of stress, including infection, trauma, boarding, or surgery.
Screening for Hypoadrenocorticism with Baseline Cortisol
One of the most common tests used for initial screening of Hypoadrenocorticism is the baseline cortisol test. This blood test measures dogs' baseline cortisol levels under normal conditions. The primary purpose of this test is to rule out Hypoadrenocorticism when cortisol levels are above a clinical decision point.
A thorough understanding of a test's specificity will enable veterinary teams to appreciate its clinical usefulness. Specificity refers to the test's ability to correctly identify dogs that do not have Hypoadrenocorticism. Baseline cortisol testing only has a high specificity of 91% when results are < 1 µg/dL ≈ 27.6 nmol/L, but specificity drops to 63% if results are 2 µg/dL ≈ 55.2 nmol/L. However, this test has 100% sensitivity, meaning that if a patient has a resting cortisol greater than 2 µg/dL ≈ 55.2 nmol/L, the patient is highly unlikely to have Hypoadrenocorticism, and further testing is rarely required.
While baseline cortisol is a practical screening test, it is not a definitive measure. A screening showing low baseline cortisol indicates potential adrenal insufficiency and requires further testing with an ACTH stimulation test—the gold standard for diagnosing Hypoadrenocorticism.
With more recent advancements in diagnostic technology, real-time cortisol testing is available for veterinary practices. This allows for almost immediate results during an exam, enabling faster decision-making in suspected cases and for earlier diagnosis in emergencies.
Screening for Hypoadrenocorticism in Chronic GI Workups
Veterinarians should always consider Hypoadrenocorticism when evaluating chronic gastrointestinal signs, especially in dogs experiencing recurrent vomiting, diarrhoea, weight loss, or a lack of appetite.
In these cases, a chronic GI workup should include a baseline cortisol test. If the baseline cortisol level is low or borderline, indicating possible Hypoadrenocorticism, additional testing with an ACTH stimulation test is necessary.
Early Identification Improves Patient Outcomes
Vague and common clinical signs make diagnosing Hypoadrenocorticism challenging. Veterinary teams often overlook signs such as chronic GI distress, stress-related flare-ups, lethargy, and PU/PD when performing tests. However, by maintaining a high index of suspicion and using strategic diagnostics, veterinarians can detect this disease early, transforming a crisis into a manageable condition.
As veterinarians identify more cases earlier, patient outcomes will improve, and veterinary teams will gain confidence in recognising and treating "the great pretender."
References:
Kintzer, P. P., & Peterson, M. E. "Diagnosis of canine Addison's disease: Sensitivity of different diagnostic tests." Journal of the American Veterinary Medical Association, vol. 250, no. 1, 2017, pp. 56-62.
Peterson, M. E., & Kintzer, P. P. "Diagnosis of Addison's disease in dogs: ACTH stimulation test revisited." Journal of the American Veterinary Medical Association, vol. 246, no. 8, 2015, pp. 900-904.
Kooistra, H. S., & van der Meer, F. "Hypoadrenocorticism: Pathophysiology and clinical diagnosis." Journal of Endocrinology and Metabolism, vol. 15, no. 4, 2018, pp. 228-236.
McAlister, E. "Addison's disease in dogs." Veterinary Practice News, 2017, Retrieved from https://www.veterinarypracticenews.com.
Simpson, K. W., & Rishniw, M. "Canine hypoadrenocorticism." Veterinary Clinics of North America: Small Animal Practice, vol. 49, no 3, 2019, pp. 463-475.
Bovens, C., et al. "Basal serum cortisol concentration as a screening test for hypoadrenocorticism in dogs." Journal of Veterinary Internal Medicine, vol. 28, no. 5, 2014, pp. 1541–1545.
Natalie Marks
Natalie Marks
5-minute read | Feb 23, 2026
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