Diagnosing Cushing’s disease in dogs is not a one-test affair. There is no single blood draw or scan that confirms it outright. Instead, veterinarians work through a layered process: suspicious clinical signs lead to routine bloodwork, which leads to one or more hormone-based screening tests, and sometimes to imaging or further differentiation tests. Each step narrows the likelihood, and the whole sequence can take weeks and cost hundreds to thousands of dollars. Understanding why the process is so involved helps make sense of the vet visits, the repeat blood draws, and the bills that come with them.
Clinical Signs That Start the Conversation
The diagnostic journey almost always begins with a dog owner noticing something off. The classic signs of Cushing’s disease (also called hyperadrenocorticism) tend to develop gradually, which is why many owners chalk them up to normal aging. Increased thirst and urination are usually the first red flags. A dog that suddenly needs to go outside at 3 a.m. or empties its water bowl twice a day gets noticed. A pot-bellied appearance, thinning skin, and symmetrical hair loss along the trunk often follow. Some dogs develop recurring skin infections or seem perpetually hungry.
Not every dog shows the textbook picture, though. Some present with only one or two signs, and certain breeds have their own patterns. Miniature poodles, for instance, sometimes show mainly hair loss and liver enzyme changes without the dramatic thirst and urination that vets typically associate with Cushing’s.
Vets also see iatrogenic Cushing’s syndrome, where the symptoms come not from the dog’s own hormone production but from long-term corticosteroid medications prescribed for allergies, inflammatory conditions, or immune-mediated diseases. In those cases, the clinical signs resolve when the medication is tapered off, and the full diagnostic workup for a tumor is unnecessary.1PubMed Central. Diagnosis and outcome of a dog with iatrogenic hyperadrenocorticism and secondary pulmonary mineralization
What Routine Bloodwork and Urinalysis Reveal
Before running any Cushing’s-specific hormone tests, most vets start with a standard chemistry panel, a complete blood count, and a urinalysis. These won’t confirm the disease on their own, but they provide strong supporting clues and help rule out other conditions that mimic Cushing’s.
The liver enzyme alkaline phosphatase, commonly abbreviated ALP, is elevated in the vast majority of affected dogs. One study of dogs with confirmed pituitary-dependent Cushing’s found ALP was increased in about 92% of cases, with the liver enzyme ALT elevated in roughly 76% and total cholesterol high in about 80%.2Journal of Veterinary Medical Science. Efficacy of Transsphenoidal Surgery on Endocrinological Status and Serum Chemistry Parameters in Dogs with Cushing’s Disease An ALP spike in a middle-aged or older dog with increased thirst is one of the strongest nudges toward further Cushing’s testing.
Urinalysis adds another piece. Dogs with Cushing’s tend to produce very dilute urine because the excess cortisol interferes with the kidneys’ ability to concentrate it. A consistently low urine specific gravity, combined with elevated liver enzymes and clinical signs, moves the suspicion from “maybe” to “probably worth testing.” Dilute urine also predisposes these dogs to urinary tract infections, which sometimes occur without obvious symptoms. One study found subclinical bacteriuria in about 12% of dogs with hypercortisolism, a rate linked to low urine concentration and low lymphocyte counts.3PubMed. Clinical and microbiological characterization of subclinical bacteriuria and sporadic bacterial cystitis in dogs with spontaneous hypercortisolism
The Three Main Screening Tests
Once a vet’s clinical suspicion is high enough, the next step is a hormone-based screening test. Three options dominate veterinary practice, each with its own strengths and blind spots. None of them is perfect, and vets often choose based on the individual case, their clinic’s capabilities, and what they’re trying to learn.
Urine Cortisol-to-Creatinine Ratio
The urine cortisol-to-creatinine ratio, or UCCR, is the simplest to collect. The owner gathers a morning urine sample at home over two consecutive days, which avoids the stress-related cortisol spikes that can happen during a vet visit. The ratio reflects average cortisol output over several hours rather than a single snapshot.
The test is quite sensitive, meaning it catches most dogs that actually have Cushing’s. One widely cited study found its sensitivity was 92%, with specificity high (95-97%) in healthy dogs and dogs suspected of Cushing’s but much lower (only 21%) in dogs with other moderate to severe illnesses. In that sicker group, 79% had false-positive results.4Journal of Veterinary Internal Medicine. Evaluation of a Urine Cortisol:Creatinine Ratio as a Screening Test for Hyperadrenocorticism in Dogs In practical terms, a normal UCCR makes Cushing’s very unlikely. But an elevated UCCR in a dog with another active illness doesn’t necessarily mean Cushing’s is present.
More recent work using automated lab methods has reported similar performance, with one study finding roughly 86% sensitivity and 63% specificity, supporting the UCCR as a reasonable first-line test to rule the disease out rather than rule it in.5Veterinary Clinical Pathology. Diagnostic cut‐off values for the urinary corticoid:creatinine ratio for the diagnosis of canine Cushing’s syndrome using an automated chemiluminescent assay The underlying principle holds up well in research: changes in cortisol secretion track reliably with changes in the UCCR, though the test is less able to distinguish between normal and below-normal cortisol levels.6Domestic Animal Endocrinology. Changes in adrenal cortisol secretion as reflected in the urinary cortisol/creatinine ratio in dogs
Low-Dose Dexamethasone Suppression Test
The low-dose dexamethasone suppression test, or LDDST, is the most commonly used screening test in general practice. The dog receives a small injection of dexamethasone (a synthetic steroid), and blood samples are drawn at baseline, four hours, and eight hours. In a healthy dog, the dexamethasone tells the brain to shut off its signal to produce cortisol, and levels drop. In a dog with Cushing’s, the cortisol stays stubbornly high.
This test has good sensitivity and can sometimes offer additional clues about whether the Cushing’s is pituitary-driven. A study that re-examined LDDST response patterns found that about 52% of dogs with confirmed Cushing’s showed no suppression at all, while about 26% showed partial suppression and roughly 10% had an “escape” pattern where cortisol dropped at four hours but bounced back by eight hours.7PubMed Central. Patterns of the low‐dose dexamethasone suppression test in canine hyperadrenocorticism revisited Among dogs without Cushing’s, about 81% showed full suppression, making a non-suppressing result fairly telling.
A separate evaluation found that at the most discriminating cut-point for the eight-hour cortisol concentration, sensitivity was about 85% and specificity reached 100%, though this was in a selected referral population.8Journal of Small Animal Practice. Re‐evaluation of the low‐dose dexamethasone suppression test in dogs The LDDST’s main limitation is the time commitment: the dog needs to stay at the clinic for roughly eight hours.
ACTH Stimulation Test
The ACTH stimulation test measures how the adrenal glands respond to a synthetic version of the hormone that naturally tells them to produce cortisol. Blood is drawn before and about an hour after an injection of synthetic ACTH. A dog with Cushing’s typically produces an exaggerated cortisol response.
This test is faster (about an hour start to finish) and tends to have good specificity when clinical suspicion is already high, meaning a positive result usually means the disease is genuinely present.9PubMed. Interpretation of laboratory tests for canine Cushing’s syndrome Its sensitivity, however, is lower than the LDDST’s, so a normal result doesn’t reliably rule Cushing’s out. One study using a low-dose depot formulation of ACTH found that the post-stimulation cortisol was elevated in about 90% of dogs with Cushing’s overall, with roughly 96% sensitivity for pituitary-dependent disease but only about 63% for adrenal tumors.10PubMed. Evaluation of the ACTH stimulation test using a low dose of a depot formulation in healthy dogs and in dogs with untreated Cushing’s syndrome That difference matters, because missing an adrenal tumor has different treatment implications than missing early pituitary disease.
The ACTH stimulation test is also the standard test for diagnosing iatrogenic Cushing’s, because dogs on long-term steroids have suppressed adrenal glands that respond weakly to stimulation. And it doubles as a monitoring tool once treatment begins, though newer evidence suggests other cortisol measurements may be equally useful for that purpose.
Figuring Out the Underlying Cause
Once a screening test supports the diagnosis, the next question is why the cortisol is elevated. About 80 to 85% of naturally occurring cases are pituitary-dependent, meaning a small tumor in the pituitary gland at the base of the brain is overproducing the hormone that drives cortisol secretion. Most of the remaining cases involve a tumor on one of the adrenal glands themselves. One Australian study found pituitary-dependent disease in about 94% of its 200-dog cohort, with adrenal tumors accounting for only about 2.5%, though breed demographics in that population (Maltese dogs made up 19%) may have skewed the ratio.11Australian Veterinary Journal. Patient signalment and aetiology of hypercortisolism in Australian dogs with Cushing’s syndrome
The distinction matters because treatment differs: pituitary-dependent disease is usually managed with medication (trilostane or mitotane), while adrenal tumors may be surgical candidates. The LDDST itself can sometimes help. If cortisol partially suppresses at the four-hour mark but rises again by eight hours, that pattern points toward pituitary disease. But if cortisol stays flat throughout, the test can’t tell you which type you’re dealing with.
The high-dose dexamethasone suppression test used to be a standard differentiating tool. Dogs with pituitary-dependent Cushing’s often show cortisol suppression at higher dexamethasone doses, while dogs with adrenal tumors do not. A large study found that when dogs met suppression criteria on the high-dose test, 135 of 137 turned out to have pituitary disease and only 2 had adrenal tumors. Around 12% of pituitary cases suppressed on the high-dose test but not on the low-dose version, meaning the high-dose test added diagnostic value beyond what the initial screening test revealed.12PubMed. Use of low- and high-dose dexamethasone tests for distinguishing pituitary-dependent from adrenal tumor hyperadrenocorticism in dogs
In current practice, though, abdominal ultrasound has largely replaced the high-dose dexamethasone test as the go-to differentiating tool. A survey of veterinarians across several European countries found that about 81% always use abdominal ultrasound for differentiation, compared to about 46% who use the LDDST pattern and fewer than 9% who use the high-dose dexamethasone test.13PubMed Central. Diagnosis of naturally-occurring Cushing’s syndrome by primary care veterinarians in selected European countries Measuring the dog’s own endogenous ACTH level is another option (a suppressed level points to an adrenal tumor, while a normal or elevated level suggests pituitary origin), but only about 11% of surveyed vets reported routinely using it, partly because the sample requires special handling and fast processing.
Imaging the Adrenals and the Brain
Abdominal ultrasound gives the vet a direct look at the adrenal glands. In pituitary-dependent disease, both adrenal glands tend to be symmetrically enlarged because they’re both being over-stimulated. An adrenal tumor, by contrast, typically shows one enlarged gland while the opposite gland is small or atrophied, since the tumor’s excess cortisol production suppresses the brain’s hormonal signal to the other side.
Ultrasound also lets the vet check for tumor invasion into surrounding structures. In one study of dogs with adrenal tumors, nearly 89% had invasion into the large vein near the adrenal gland (the caudal vena cava), which significantly affects whether surgery is feasible.14PubMed Central. The use of ultrasonographic adrenal dimensions and the adrenal dimension-to-aorta ratio in the diagnosis of benign and malignant adrenal diseases in dogs The interpretation is not always straightforward, though. Occasionally, a dog with pituitary-dependent disease has asymmetric adrenal glands, or a dog has concurrent pituitary and adrenal changes. One imaging study confirmed that some dogs with spontaneous hypercortisolism have both pituitary and adrenal lesions visible on CT.15PubMed Central. Concurrent pituitary and adrenocortical lesions on computed tomography imaging in dogs with spontaneous hypercortisolism
Advanced imaging of the brain, with CT or MRI, becomes relevant when a pituitary tumor is suspected, particularly to determine its size. Large pituitary tumors (macroadenomas) that extend above the sella turcica, the bony pocket where the pituitary sits, can press on the brain and cause neurological signs. The definition of “macro” varies somewhat across studies, but the key clinical question is whether the tumor is big enough to warrant radiation therapy or affect prognosis.16Journal of Veterinary Internal Medicine. Effect of pituitary-dependent hypercortisolism on the survival of dogs treated with radiotherapy for pituitary macroadenomas Brain imaging is expensive and usually requires anesthesia, so it’s typically reserved for dogs where the treatment plan would change based on what the scan shows.
When the Tests Don’t Cooperate
Cushing’s diagnosis gets genuinely tricky in several common scenarios. Dogs with moderate to severe concurrent illnesses can have elevated cortisol from stress alone, producing false-positive results on every screening test. This is why most endocrinology guidelines emphasize that testing should be reserved for dogs in whom Cushing’s is strongly suspected based on signs and basic bloodwork, not used as a fishing expedition on any sick dog.
On the other end, some dogs show convincing clinical signs of Cushing’s yet come back normal on standard screening tests. This presentation has been called “atypical” or “occult” Cushing’s syndrome. The theory is that these dogs may be overproducing adrenal sex hormones (like progesterone or estradiol) rather than cortisol, which the standard tests don’t measure.17PubMed. Atypical Cushing’s syndrome in dogs: arguments for and against The concept remains controversial among veterinary endocrinologists, with strong voices on both sides about whether it’s a real entity or a collection of other diagnoses being lumped together.
Dogs with suspected sex-steroid excess often look different from classic Cushing’s patients. They may present primarily with skin problems or reproductive abnormalities rather than the trademark excessive thirst and urination. Certain breeds, including miniature poodles, appear overrepresented. The most telling lab finding is still elevated liver enzymes, but the hormonal workup requires a specialized adrenal panel that measures multiple steroid hormones before and after ACTH stimulation.18PubMed. Hyperadrenocorticism associated with sex steroid excess
Rare cases defy the usual diagnostic logic entirely. One published case involved a dog whose adrenal tumor was producing ACTH locally within the gland itself, making the initial test results look like typical adrenal-dependent disease. The clue that something unusual was happening came when ultrasound showed the opposite adrenal gland was enlarged rather than shrunken, which contradicted the expected pattern of adrenal suppression.19PubMed Central. Cushing’s syndrome caused by intra‐adrenocortical adrenocorticotropic hormone in a dog Cases like these are exceptional, but they illustrate why vets sometimes need multiple overlapping tests to arrive at the right answer.
The Financial Reality of Diagnosis
Cushing’s disease testing is expensive relative to many routine veterinary diagnostics. A single LDDST or ACTH stimulation test can cost $150 to $300 or more depending on the clinic, and most dogs need at least two or three tests across the screening and differentiation stages. Add ultrasound, and the total can climb past $1,000 before treatment even begins. Research has found that insured dogs are roughly four times more likely to be diagnosed with Cushing’s than uninsured dogs, suggesting a substantial level of under-diagnosis driven by the cost of reaching a definitive answer. Multiple tests are often performed in primary-care settings, compounding the financial burden, and when tests are run on dogs with only moderate suspicion, the ambiguous results can generate even more testing.
Some owners and vets opt for a pragmatic approach: if clinical signs, bloodwork, and one screening test are all pointing the same direction, they start a trial of treatment with trilostane and monitor the response rather than pursuing every available differentiating test. This is especially common in older dogs with classic presentations where the pre-test probability of pituitary-dependent disease is already very high.
Monitoring Once Treatment Begins
Diagnosis doesn’t end when the label is applied. Dogs on trilostane, the most commonly prescribed medication for pituitary-dependent Cushing’s, need regular monitoring to ensure the drug is controlling cortisol production without overshooting into dangerously low levels. For years, the standard monitoring protocol has been an ACTH stimulation test performed four to six hours after the morning trilostane dose.
That recommendation is facing some scrutiny. A study comparing three cortisol measurements (a pre-trilostane cortisol level, a three-hour post-trilostane cortisol level, and the traditional post-ACTH stimulation cortisol) against a clinical score based on owner-reported signs found that the pre-trilostane and three-hour post-trilostane cortisol values correlated better with how the dog was actually doing at home. The sensitivity and specificity for distinguishing well-controlled from poorly controlled dogs were superior to the post-ACTH stimulation cortisol.20Veterinary Record. Pre‐trilostane and three‐hour post‐trilostane cortisol to monitor trilostane therapy in dogs For owners, this is practical good news, since a simple blood draw timed to the trilostane dose is faster and cheaper than a full ACTH stimulation test.
Regardless of which monitoring method the vet uses, the owner’s observations remain critical. Changes in water intake, energy level, appetite, and coat quality often signal shifts in disease control before lab numbers do. Many vets now use structured questionnaires or symptom diaries to formalize that feedback, giving them a more complete picture alongside the bloodwork.
Breed Patterns and Who Gets Tested
Cushing’s disease most often affects middle-aged to older dogs, typically those over eight years old. Certain small and medium-sized breeds show up disproportionately: poodles, dachshunds, terrier breeds, and beagles are frequently cited. In the Australian cohort mentioned earlier, Maltese dogs accounted for 19% of diagnoses and were overrepresented compared to the general dog population. Those Maltese were also diagnosed at a younger age than other breeds.11Australian Veterinary Journal. Patient signalment and aetiology of hypercortisolism in Australian dogs with Cushing’s syndrome
Large-breed dogs can develop Cushing’s too, but they’re more likely to have adrenal tumors than pituitary disease, and the clinical signs may be less obvious against the backdrop of age-related changes in bigger dogs. Breed information helps vets calibrate their index of suspicion, but it doesn’t change the testing pathway itself. A dachshund with classic signs and elevated ALP gets the same LDDST as a Labrador, though the vet may already be mentally placing a higher probability on a positive result for the dachshund before the numbers come back.