Normal ACTH stimulation test with suspected Cushing's in the dog
11-year-old neutered male Yorkshire Terrier with polyuria/polydipsia, polyphagia, thin skin and a pot belly. Bloods show ALP of 1,250 U/L, high cholesterol and urine specific gravity 1.008.
| Parameter | Result | Reference |
|---|---|---|
| Basal cortisol | 4.8 µg/dL | 1.0–6.0 |
| Cortisol 1 h post-ACTH | 15.6 µg/dL | 6.0–17.0 |
| Alkaline phosphatase | 1,250 U/L | 20–150 |
What is the most appropriate next step?
chevron_right Show answer and explanation
A. Perform a low-dose dexamethasone suppression test
Correct. ACTH stimulation has limited sensitivity (approx. 60–85%, lower for adrenal tumours), so a normal result does not rule out Cushing's. The low-dose dexamethasone suppression test is more sensitive and is the test of choice when clinical suspicion is high.
B. Rule out hyperadrenocorticism and look for another cause of the polyuria
With such typical signs, a normal result from a test of limited sensitivity is not enough to rule out the disease. A more sensitive test is needed before dropping the suspicion.
C. Start trilostane because the clinical picture is very suggestive
Hyperadrenocorticism is never treated on clinical grounds alone: it must be confirmed biochemically. Treating a dog without the disease risks iatrogenic hypoadrenocorticism.
D. Repeat the stimulation test with twice the dose of synthetic ACTH
The standard dose of tetracosactide already produces maximal adrenal stimulation; doubling it does not improve sensitivity. The issue is the test itself, not the dose.
lightbulb Key takeaway
ACTH stimulation is the test of choice for Addison's and for trilostane monitoring, but for diagnosing Cushing's it is less sensitive than the low-dose dexamethasone test. Its advantages are less interference from stress and the ability to detect iatrogenic Cushing's.
Test yourself with 10 random questions
Clinical pathology · 100 questions, a different test every time
Related questions
Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.