Cushing's and Addison's Disease: Cortisol and ACTH Tests

Cushing's disease means a dog's body makes too much of the hormone cortisol, and Addison's disease means it makes too little. Blood tests for cortisol and ACTH, with a stimulation or suppression test, help a vet tell them apart from other illnesses. A registered veterinarian chooses the tests that fit the dog's signs.

What are cortisol and the adrenal glands?

A dog has two small adrenal glands near the kidneys. They make cortisol, often called the stress hormone, which also helps control blood sugar, energy and the way the body copes with illness. A small gland in the brain, the pituitary, makes ACTH, a hormone that tells the adrenals when to make more cortisol.

This pair works like a thermostat. When it slips, cortisol can run too high, which is Cushing's disease, or too low, which is Addison's disease. Cushing's is seen mostly in middle-aged and older dogs. A small growth on the pituitary or on an adrenal gland is a common reason, and the vet's job is to find which.

Which signs point to which disease?

A dog with Cushing's disease may show:

• more thirst, more urine and a big appetite
• a pot belly and thinning hair on the body
• thin skin, panting and tiring easily

A dog with Addison's disease may show:

• weakness, vomiting, loose motions and poor appetite
• weight loss and shaking
• signs that come and go, which makes the illness easy to miss

A sudden collapse is an emergency, so go to a vet at once. Many other illnesses, such as kidney disease and diabetes, cause similar signs, so guessing at home is risky. A lab test is how vets sort these out.

Which cortisol tests do vets choose?

A resting cortisol test checks one sample at one moment. The general Cortisol test and the Canine Cortisol (cCortisol) test, which is made for dogs, both measure it. In a dog that might have Addison's disease, a resting level that is clearly not low makes it much less likely. A low level usually needs a second test to confirm.

That second test is often the ACTH Stimulation Test. Cortisol is measured before and after the vet gives an injection of ACTH, to see how well the adrenal glands respond. In Addison's disease the response is weak. Vets may also use this test later, to follow the dog over time.

For suspected Cushing's disease, the Low-dose Dexamethasone Suppression Test (LDDST) is commonly used. Normally a small steroid injection makes the body lower its own cortisol. The vet takes blood before the injection and again at set times afterwards, and the lab or vet explains the timing. If cortisol does not fall as expected, that may indicate Cushing's disease.

What does the ACTH test add?

The ACTH test measures the pituitary hormone itself. Once Cushing's disease looks likely, it can help the vet judge whether the problem begins in the pituitary or in an adrenal gland, and that guides the next steps. ACTH breaks down easily in a sample, so it needs careful handling. Ask the lab how to collect and carry it.

What can confuse the results?

Cortisol rises with stress, fear and other illness, so a nervous dog or a dog sick with another disease may give a misleading result. For this reason these tests are meant for dogs whose signs fit, not for routine screening of healthy dogs.

Steroid medicines can also change the results, and they can cause signs like Cushing's disease on their own. Tell your vet about every product your dog has had, including tablets, injections, ear drops, eye drops and skin creams. No single test is perfect, so a vet may repeat a test or combine more than one. A normal result does not always rule a disease out.

Read next

Weakness and vomiting have many causes, and infection is one of them, so Leptospirosis Tests in Dogs and Cattle explains the tests used for leptospirosis in dogs. Lab reports also use different methods, and RT-PCR, Rapid Kit or ELISA: Which Test for My Pet? helps you understand what a rapid kit, an ELISA and an RT-PCR each tell you.

Testing in Bhopal

For hormone tests, the sample timing and tube matter, so call the lab first and plan the visit with your vet. Free sample collection is available anywhere in Bhopal, and the lab is at C-200, C Sector, Shahpura. If you live in another district, your vet can send the samples by courier or bus parcel. The number is +91 88175 01118 for calls and WhatsApp, and the lab confirms the method, sample needs and reporting time when you book.