Cushing's Disease in Dogs Test: ACTH Stim, LDDS, Blood Work

Cushing's disease in dogs is diagnosed in stages, not with a single blood test. Book a veterinary appointment before anything else, and if your dog is collapsing, vomiting repeatedly, breathing with difficulty, straining to urinate without producing anything, or suddenly weak, go to an emergency clinic now rather than waiting for a scheduled test. For a stable dog showing the familiar picture of heavy drinking, frequent urination, a ravenous appetite, panting and a sagging belly, the process runs in a predictable order: history and physical exam, screening blood work and urinalysis, a confirmatory hormone test such as the low dose dexamethasone suppression (LDDS) test or an ACTH stimulation test, and then imaging to work out which form of the disease is present.

There is no reliable at-home test for this condition, and no single number on a routine panel settles it. Every step below happens at a veterinary clinic, and the order matters, because testing a dog who does not have the right clinical picture tends to produce confusing answers rather than useful ones.

Why there is no simple yes or no test

Cushing's disease, properly called hyperadrenocorticism, means the body is exposed to too much cortisol for too long. Cortisol is the same hormone that rises when a dog is frightened, in pain, dehydrated or fighting another illness. That is the central problem with testing: a cortisol measurement taken at a single moment tells you about that moment, not about the months of excess that cause the disease.

So veterinarians treat the clinical picture as the first and most important piece of evidence. The signs that raise suspicion include dramatically increased thirst and urination, a bottomless appetite, heavy panting, a pot-bellied appearance, thinning skin, symmetrical hair loss along the flanks and trunk, slow healing, muscle weakness and repeated skin or urinary infections. Most dogs diagnosed are middle-aged or older.

No single blood test confirms Cushing's disease on its own: the diagnosis comes from the combination of your dog's clinical signs, screening blood work and a hormone test your veterinarian chooses for that specific picture.

There are three broad causes, and they matter for testing. The pituitary form, driven by a small benign tumour in the pituitary gland that overstimulates both adrenal glands, is the most common. The adrenal form involves a tumour on one adrenal gland itself. The third form is iatrogenic, meaning it is caused by steroid medication the dog has been given, whether tablets, injections, eye drops, ear drops or skin creams. Bring a complete list of everything your dog has received to the appointment, because that history can change which test is run and how the result is read.

What routine blood work and urinalysis usually show

Screening panels do not diagnose Cushing's, but they build the case and rule out the conditions that look like it. Expect a complete blood count, a biochemistry panel and a urinalysis, often with blood pressure measurement.

Finding on blood work or urine	What it can point to
Markedly raised alkaline phosphatase (ALP)	The most common abnormality in dogs with Cushing's, but also seen with liver and gallbladder disease, bone turnover in young dogs, and steroid medication
Mildly raised ALT	Liver cells under strain; non-specific on its own
Raised cholesterol and triglycerides	Altered fat metabolism, which excess cortisol can drive; also seen with hypothyroidism or a recent meal
Raised blood glucose	Cortisol opposes insulin; marked elevation raises the question of diabetes alongside Cushing's
Low blood urea nitrogen	Often reflects the constant drinking and dilute urine
Stress leukogram (higher neutrophils and monocytes, lower lymphocytes and eosinophils)	A classic steroid pattern, though any stressed or ill dog can show it
Dilute urine with low specific gravity	Consistent with Cushing's, but also with kidney disease, diabetes and several other conditions
Protein in the urine, or infection with no outward symptoms	Common companions of Cushing's; cortisol blunts the usual inflammatory signs

When owners search for what their blood work results mean, this is the honest answer: these values make the disease more or less likely, and they flag problems that need managing in their own right. They do not confirm anything. A dog can have a strikingly high ALP and no endocrine disease at all, and results vary from dog to dog. Your veterinarian reads the panel as a pattern against the physical exam, not as a checklist.

The confirmatory tests your veterinarian may choose

If the picture fits, the next step is a dynamic hormone test, meaning the clinic measures cortisol, intervenes, then measures again to see how the system responds. Which test gets chosen depends on the suspected cause, the dog's other health problems, how long the dog can stay at the clinic and local laboratory turnaround. Costs vary widely by clinic and region, so ask for an estimate when you book.

Test	What it measures	Where it is strongest	Main limitation
Urine cortisol to creatinine ratio (UCCR)	Cortisol relative to creatinine in urine, often collected calmly at home	Ruling the disease out when the result is normal	Easily raised by stress and unrelated illness, so a high result alone confirms nothing
Low dose dexamethasone suppression (LDDS)	Whether a small dose of synthetic steroid switches off the dog's own cortisol production the way a healthy system should	Confirming the disease in a dog with typical signs, and sometimes suggesting the pituitary form from the suppression pattern	Requires most of a working day in hospital; other illnesses can distort the result
ACTH stimulation test	How much cortisol the adrenal glands release when prompted with synthetic ACTH	Identifying steroid-induced (iatrogenic) Cushing's, and monitoring dogs already on treatment	Can miss genuine cases, so a normal result does not always close the question
Abdominal ultrasound	The size, shape and symmetry of both adrenal glands, plus the liver and urinary tract	Separating a tumour on one adrenal gland from the pituitary form	Operator dependent, and it does not confirm the hormone diagnosis by itself

In practice, the LDDS is the test many veterinarians reach for first when they want to confirm the disease, because it rarely misses an affected dog. Your dog stays at the clinic, a baseline blood sample is taken, a small dose of dexamethasone is given, and further samples are drawn at set intervals through the day. The ACTH stimulation test is quicker, involves a baseline sample followed by an injection and a second sample at a set interval afterwards, and it is the better choice when steroid medication is the suspected cause or when treatment is being monitored.

The UCCR sits earlier in the sequence. Research suggests it is far more useful for ruling the disease out than for confirming it, which is why a normal result is reassuring while a raised one usually leads to one of the other two tests. Collecting that sample at home, in the garden, first thing in the morning, helps keep stress out of the number.

Making sense of borderline and confusing results

Laboratories report cortisol against reference intervals, and interpretation is about the pattern across samples rather than any one figure. Results land in roughly three territories: clearly consistent with the disease, clearly not, and the grey zone in between.

Grey-zone results are common and are not a failure of the test. Any significant illness elsewhere in the body, from a dental infection to kidney disease, can push cortisol testing towards a false positive, which is why veterinarians prefer to test a dog who is otherwise stable. Dogs who find the clinic stressful can also skew results. The usual response is to treat or resolve the other problem, then retest after an interval, rather than starting lifelong treatment on an ambiguous number.

There is also a less common presentation sometimes called atypical Cushing's, where the standard tests do not line up with a dog who looks clinically affected. In those cases a veterinarian may send a broader adrenal hormone panel to a specialist endocrinology laboratory, or refer to an internal medicine specialist. If testing has been inconclusive twice, asking about referral is a reasonable thing to raise. Talk to your vet about what a repeat test would add before agreeing to it.

Identifying the type, and what comes next

Confirming the disease is only half the diagnostic job. Because the pituitary and adrenal forms are managed differently, the next stage is identifying which one is present. Abdominal ultrasound is the usual tool, looking for two evenly enlarged adrenal glands versus one mass with the opposite gland shrunken. Measuring the dog's own circulating ACTH, or running a high dose dexamethasone suppression test, can help when ultrasound is equivocal. Advanced imaging of the head with CT or MRI is reserved for specific situations, such as neurological signs or planning specialist treatment.

Alongside this, your veterinarian will want to know what else is going on. Dogs with Cushing's frequently carry high blood pressure, protein loss through the kidneys, silent urinary tract infections, or diabetes, and each of those needs its own plan. Once treatment begins, monitoring tests are repeated at intervals the veterinarian sets, because the goal is controlling signs without swinging too far the other way.

Key Takeaways

• Diagnosis is a sequence: clinical signs, then screening blood work and urinalysis, then a confirmatory hormone test, then imaging to identify the form.
• Routine blood work supports suspicion rather than proving anything; a high ALP is the most common clue but has many other causes.
• The LDDS test is a common first confirmatory choice, while the ACTH stimulation test is favoured when steroid medication is suspected or when monitoring treatment.
• The urine cortisol to creatinine ratio is better at ruling the disease out than ruling it in.
• Other illnesses and plain stress can push cortisol results upward, so testing a stable dog gives cleaner answers.
• Borderline results often mean retesting later or referral, not immediate treatment.
• There is no at-home test, and results vary from dog to dog.

Your veterinarian owns the diagnosis and the treatment plan here. They decide which test fits your dog, how to read the result against everything else on the chart, and what happens afterwards, including any prescribed medication and the monitoring schedule that goes with it. Your job is the part only you can do: track water intake, note appetite and accidents, photograph coat changes over time, and bring a complete medication history to every appointment. That record often shapes the testing decision more than any single number does.

For help telling an urgent problem from one that can wait for a scheduled appointment, see Dog Emergency Signs.