There are several diagnostic procedures used to confirm Cushing’s disease. Because its symptoms are relatively generic and can point to many other conditions, your veterinarian will often use more than one test, both to confirm the disease and to work out which type it is.
Bloodwork and Urinalysis
The work-up usually begins with a complete blood count (CBC), a blood chemistry panel and a urinalysis. These do not diagnose Cushing’s on their own, but they reveal supportive clues — commonly a markedly elevated alkaline phosphatase (ALP), increased cholesterol, and dilute urine. A urinalysis may also uncover a urinary tract infection, which is common in these dogs.
Urine Cortisol:Creatinine Ratio
This is a helpful screening test. You collect a urine sample from your dog at home — ideally away from the stress of the clinic, since stress can raise cortisol and skew results — and your vet sends it to a laboratory. A normal result makes Cushing’s unlikely, so the test is most useful for helping to rule the disease out rather than to confirm it.
ACTH Stimulation Test
The ACTH stimulation test measures how the adrenal glands respond when given a dose of synthetic ACTH. Blood cortisol is measured before and after. It is widely used both to help confirm the diagnosis and, importantly, to monitor treatment once therapy has begun.
Low-Dose Dexamethasone Suppression Test
The low-dose dexamethasone suppression test (LDDS) is another common and sensitive test. The dog is given a low dose of dexamethasone, and cortisol is measured several hours later. In a healthy dog, cortisol drops; in a dog with Cushing’s, it fails to suppress normally. This test can sometimes also help distinguish pituitary-dependent from adrenal-based disease.
Abdominal Ultrasound
An abdominal ultrasound lets the veterinarian study the size and shape of the adrenal glands and other organs. If both adrenal glands are enlarged, pituitary-dependent disease is more likely; if one adrenal gland is enlarged and the other is small, an adrenal tumor is more likely. Ultrasound also helps assess the liver and screen for other problems.
Putting the Results Together
Your veterinarian interprets all of these results alongside your dog’s history and physical exam. Sometimes additional tests — such as measuring endogenous ACTH or advanced imaging — are used to pinpoint the type. This careful, step-by-step approach is what allows for the right treatment plan. Veterinary teaching hospitals, such as those at Cornell University’s College of Veterinary Medicine, are excellent resources if your case is complex or a referral is suggested.