Vet‑Approved 2025 Guide: ACTH Stimulation Test for Dogs – Diagnosis, Interpretation & Home Care 🐶🩺💉

By Dr. Duncan Houston BVSc

The ACTH stimulation test is an essential hormone test used to diagnose potential adrenal disorders such as Addison’s disease (low cortisol) and iatrogenic Cushing’s (from steroids), and to monitor treatment for Cushing’s disease. In this 2025 vet‑approved guide, we’ll walk through why we need it, how it’s done, interpreting results, preparation, risks, cost, and supportive care, with calm tools from Ask A Vet, to make the process smoother for dogs and owners alike. 🐾🧬

🔍 Purpose of the Test

The test measures how well the adrenal glands respond to synthetic ACTH (cosyntropin). It’s most accurate in identifying:

Addison’s disease (hypoadrenocorticism): Addison’s dogs exhibit low cortisol before and after stimulation.
Iatrogenic Cushing’s (from long-term steroid use): Dogs show a blunted or flat cortisol response after ACTH challenge.
Monitoring treatment for Cushing’s (such as trilostane or mitotane): Helps vets adjust medication dosage for optimal control.

📅 When Is It Recommended?

— At the first suspicion of Addison’s or iatrogenic Cushing’s, especially with symptoms like lethargy, appetite change, increased thirst or urination.
— After starting treatment for Cushing’s, typically 10–14 days post-initiation, then 30 days, 90 days, and every 3–4 months.

🛠️ How the Test Works: Step-by-Step

Baseline sample: Collect blood for resting cortisol.
Inject ACTH (cosyntropin): Typically 5 µg/kg IV or IM; gel option also available.
Post-stimulation sample: For IV injection: draw blood 1 hour later. For gel: additional draw at 2 hours.
Lab analysis: Compare cortisol before and after stimulation to assess adrenal function.

📈 Interpreting Results

Addison’s disease: Baseline and post-ACTH cortisol usually ≤2 µg/dL (dogs may be even <1 µg/dL).
Iatrogenic Cushing’s: Flattened cortisol rise—low baseline and minimal increase after stimulation.
Adjusting medication (trilostane/mitotane): Post-ACTH cortisol 60–200 nmol/L (approx 2.2–7.3 µg/dL) is the target; <60 nmol/L suggests over-suppression, >200 nmol/L may indicate inadequate control.
Natural Cushing’s screening: Only moderately sensitive—misses ~20% of pituitary and ~40% of adrenal cases—LDDST is often preferred.

⚠️ Risks & Considerations

The ACTH test is generally safe. Potential issues include mild allergic reactions to cosyntropin (<1%), minor anxiety or discomfort from blood draws, and risk of nerve trauma with IM injections.

Medications such as corticosteroids can invalidate results—stop prednisone or steroid eye/ear drops for at least 24 hours before testing.

💰 Cost & Preparation

Typical cost: $150–$300, depending on clinic and lab services.
Insurance: Often covered if medically indicated (not pre-existing conditions).
Preparation: Discuss all meds with vet. No fasting usually needed, but sedatives like trazodone may be used if your pet is anxious.

📋 Post-Test Care & Support

After the test, mild lethargy or thirst may continue but dogs generally bounce back quickly. Ensure calm rest and hydration. Use easing tools:

Ask A Vet virtual consults help interpret results, provide medication advice, and determine next steps without extra clinic visits.

🔍 Follow-up & Monitoring

If results are borderline or treatment is ongoing:

Repeat ACTH test 1–4 weeks after initial test if Addison’s is suspected but cortisol is mid-range.
Combine ACTH with other diagnostics (endogenous ACTH, electrolytes) to differentiate primary vs secondary Addison’s.
Monitor Cushing’s patients every 3–4 months with ACTH tests post-medication for dosage adjustments.

🐕 Special Cases & Breed Considerations

Young dogs: Addison's is often immune-mediated; test when symptoms like vomiting, diarrhea, weakness, and hyperkalemia appear.
Senior small breeds: More prone to hypoadrenocorticism—monitor cortisol in elderly animals.

🏁 Final Thoughts

The ACTH stimulation test remains a cornerstone of adrenal disease diagnosis and management in dogs. In 2025, paired with advanced lab support and remote vet tools like Ask A Vet, it’s easier than ever to get accurate results and build personalized treatment plans. Support your pet with calm confidence and professional guidance—your pup deserves no less. 🐶❤️

Need help interpreting results or planning treatment? Visit Ask A Vet for expert advice, and explore calming aids to make your dog’s journey smoother. 🐾✨