Hypoadrenocorticism (Addison's disease) in cats is rare but life-threatening — primary hypoaldosteronism means the adrenal glands fail to produce enough aldosterone and cortisol, sending electrolytes dangerously out of balance. Without treatment, an Addisonian crisis can be fatal within hours. Early recognition of subtle signs saves lives.
Last reviewed: June 2026
What Is Hypoaldosteronism in Cats?
Hypoaldosteronism — the signature feature of feline Addison's disease — occurs when the adrenal cortex fails to secrete adequate aldosterone, the hormone that regulates sodium and potassium balance. The result is hyperkalemia (high potassium) and hyponatremia (low sodium), a combination that slows the heart and weakens every organ system. As described in Ettinger's Textbook of Veterinary Internal Medicine, feline hypoadrenocorticism is considerably rarer than the canine form, which means it is frequently misdiagnosed for months before the true cause is found.
The adrenal glands sit just ahead of each kidney. In primary hypoaldosteronism, immune-mediated destruction, granulomatous disease, or infiltration (lymphoma, histoplasmosis) destroys adrenocortical tissue. Secondary disease arises when pituitary ACTH output fails, suppressing the cortex — these cats retain mineralocorticoid function and rarely develop the severe electrolyte crisis seen in primary cases.
Approximately 60–70% of feline Addison's cases involve young to middle-aged females, though any age or sex can be affected (AAFP-AAHA Feline Life Stage Guidelines, 2021). The peak presentation is the "Addisonian crisis" — acute collapse triggered by stress, illness, or surgery — but months of waxing-and-waning lethargy, anorexia, and weight loss often precede the crash.
Signs and Symptoms to Watch For
Because aldosterone normally tells the kidneys to retain sodium and excrete potassium, its absence flips those gradients:
- Progressive weakness and lethargy — owners often describe "he just stopped playing" over weeks
- Waxing-and-waning anorexia — the cat eats for a few days, then refuses food again
- Weight loss and muscle wasting — loss of condition despite a normal-seeming appetite on good days
- Vomiting and diarrhea — intermittent GI signs that mimic IBD or pancreatitis
- Increased thirst and urination — from sodium wasting and resulting volume depletion
- Slow heart rate (bradycardia) — hyperkalemia depresses cardiac conduction; heart rate below 140 bpm in a resting cat is a red flag
- Weak, thready pulse — poor cardiac output
- Shaking or muscle tremors — electrolyte-driven muscle dysfunction
- Acute collapse — the Addisonian crisis: the cat suddenly cannot stand, has pale or grey gums, and is barely responsive
Classic bloodwork shows hyperkalemia (K⁺ > 6.0 mEq/L), hyponatremia (Na⁺ < 130 mEq/L), and a sodium-to-potassium ratio below 27:1, as described in Nelson & Couto's Small Animal Internal Medicine.
How Your Vet Diagnoses It
No single symptom diagnoses Addison's disease — the pattern matters. Your vet will likely pursue:
- Chemistry panel — the Na:K ratio below 27 is the cardinal clue; non-regenerative anemia and elevated BUN from prerenal azotemia are common
- Urinalysis — dilute urine (USG below 1.030) despite dehydration suggests impaired concentrating ability
- Electrocardiogram — hyperkalemia produces tall spiked T-waves, wide QRS complexes, and eventually a sine-wave pattern
- ACTH stimulation test — the definitive test; a baseline cortisol below 2 µg/dL followed by a post-ACTH cortisol below 2 µg/dL confirms primary hypoadrenocorticism
- Abdominal ultrasound — may reveal bilaterally small adrenal glands in primary Addison's, or mass lesions if infiltrative disease is responsible
Differentials include renal failure, urinary obstruction, and severe cardiac disease — all can cause hyperkalemia. An ACTH stim test distinguishes them definitively.
Treatment and Long-Term Management
An Addisonian crisis is a true emergency requiring IV fluids (0.9% NaCl to correct hyponatremia and volume deficit), IV dexamethasone, and cardiac monitoring. Once stabilized, mineralocorticoid replacement begins.
Long-term options include:
- Fludrocortisone acetate — oral daily mineralocorticoid plus glucocorticoid; some cats need dose adjustments every few months
- Desoxycorticosterone pivalate (DOCP) — injectable mineralocorticoid every 25–28 days, paired with daily prednisolone for glucocorticoid replacement
- Stress dosing — during illness, surgery, or boarding, glucocorticoid doses are doubled or tripled to prevent crisis
Electrolytes should be rechecked 2–3 weeks after any dose change and every 3–6 months once stable, as outlined in Ramsey's BSAVA Manual of Small Animal Endocrinology. With consistent treatment, cats with Addison's disease live normal lifespans.
When to See a Vet
Call your vet today if:
- Your cat has had intermittent vomiting or anorexia for more than one week without a clear cause
- Your cat is losing weight despite eating, or muscle mass is visibly reduced
- Your cat seems persistently weaker or less active than normal
- Your cat's resting heart rate is below 140 bpm (check by placing a hand on the chest)
- A chemistry panel shows a Na:K ratio below 27 or potassium above 6.0 mEq/L
Go to the ER immediately if:
- Your cat collapses or cannot stand
- Gums are pale, white, grey, or blue-tinged
- Heart rate is below 100 bpm or the pulse is barely palpable
- Your cat is unresponsive or barely conscious
- Rapid deterioration within a few hours after any stressful event
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Frequently Asked Questions
What are the earliest signs of Addison's disease in cats? The earliest signs are easy to miss: intermittent anorexia lasting a day or two, mild lethargy, and occasional vomiting that waxes and wanes for weeks. Weight loss of more than 5–10% of body weight over a few weeks, combined with recurring GI upset that never fully resolves, should prompt a chemistry panel to evaluate the sodium-to-potassium ratio. Many cats are labeled as having IBD or "finicky eating" before the diagnosis is made.
How is feline Addison's disease diagnosed? Diagnosis requires an ACTH stimulation test: baseline cortisol is drawn, synthetic ACTH is injected, and cortisol is measured again 60 minutes later. In Addisonian cats, both values remain below 2 µg/dL, confirming adrenal failure. Bloodwork showing hyperkalemia, hyponatremia, and a Na:K ratio below 27:1 raises strong suspicion beforehand and warrants same-day evaluation rather than a wait-and-see approach.
Is feline Addison's disease treatable? Yes — with lifelong mineralocorticoid and glucocorticoid replacement, most cats achieve excellent quality of life and normal longevity. DOCP injections every 25–28 days plus daily oral prednisolone is a common and effective protocol. Owners learn to recognize early crisis signs and may carry emergency dexamethasone for injection when directed by their vet.
How much does diagnosing and treating Addison's disease cost? Initial diagnosis — including an ACTH stimulation test ($150–300), chemistry panel ($100–250), and urinalysis ($50–100) — typically runs $300–650. Emergency stabilization for an Addisonian crisis adds $500–1,500 for IV fluids, hospitalization, and monitoring. Long-term, DOCP injections run roughly $80–150 per dose every 4 weeks; oral fludrocortisone costs $30–80 per month. Annual follow-up bloodwork adds $150–300/year. Catching it before a crisis is dramatically cheaper than emergency care.
Can a cat have Addison's without low sodium and high potassium? Yes — secondary hypoadrenocorticism (pituitary ACTH failure) spares mineralocorticoid production, so electrolytes can be normal. These cats present mainly with GI signs and weakness from cortisol deficiency alone. An ACTH stim test is still required for diagnosis; the electrolyte panel alone will miss secondary disease.
What triggers an Addisonian crisis in cats? Any physiological stress — illness, surgery, boarding, travel, or even a painful dental procedure — can overwhelm a cat's inadequate cortisol reserve and precipitate acute collapse. This is why stress dosing (temporarily doubling the glucocorticoid dose) is critical before any procedure, and why owners of diagnosed cats should carry emergency dexamethasone.
What is the long-term prognosis for a cat with Addison's disease? With consistent medication and follow-up, the prognosis is excellent. Most cats stabilize within days to weeks of starting mineralocorticoid replacement, regain normal appetite and energy, and live out their expected lifespan. The main risk is an unrecognized crisis during illness or when medication is accidentally missed — which underscores the importance of a reliable dosing schedule and owner education about early warning signs.
How does feline Addison's differ from canine Addison's? Cats develop primary Addison's far less often than dogs, and when they do, the presentation tends to be more subtle and prolonged before crisis. The same core diagnostic approach applies — ACTH stim test, electrolyte panel — but the lower index of suspicion in cats means many are diagnosed only after an acute collapse. Treatment protocols are similar but feline-specific dosing and follow-up intervals may differ from canine guidelines as outlined in Ettinger's Textbook.
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