By Manthar Ahmad, DVM
As an experienced veterinarian specializing in pet health, I understand the challenges associated with diagnosing Cushing's disease in dogs. If your beloved pet is displaying symptoms of dog Cushing’s syndrome, you are likely to have numerous questions.
How does one test for Cushing's disease in dogs? What are the associated costs? Which test is the most accurate? From blood tests such as the ACTH Stimulation Test to the Low Dose Dexamethasone Suppression Test (LDDS), each method plays a unique role in diagnosing this complex condition.
This article is specifically curated with a clear purpose in mind to highlight the different available options in the market that you can select to get your dog diagnosed. By the end, you’ll have a clear understanding of the various testing options and their costs, and you will be better equipped to select the best possible dog Cushing’s test required for your dog.
So, let’s dive in and understand the laboratory tests for diagnosing Cushing’s syndrome in dogs together!
Urine Cortisol Ratio (UCCR) Test
A urine test for Cushing's disease in dogs, or UCCR, is a non-invasive method used in the initial screening for hyperadrenocorticism in dogs. It is an instrumental screening test, as a low (normal) result makes Cushing's highly unlikely.
Cushing's disease increases the amount of cortisol being lost in the urine. This cortisol can be measured and compared to the amount of creatinine (a substance that is excreted at a relatively constant rate, which helps to standardize the cortisol levels). This dog Cushing’s test measures the amount of cortisol in the dog's urine relative to creatinine.
If this initial screening test indicates characteristics similar to those of Cushing's disease, more extensive diagnostic tests will be required to confirm the diagnosis and establish the type of Cushing's disease that your pet has. These tests may include an adrenocorticotropic hormone (ACTH) stimulation test, low-dose dexamethasone suppression tests (LDDST), and endogenous ACTH concentrations.
Interpreting the Results
The part and process of this test would include collecting a urine sample of the dog, usually from the first urination of the day, when cortisol levels are naturally higher. The sample is then taken to a laboratory to find out the ratio of cortisol to creatinine.
A calculated ratio of less than 17.5 x 106 indicates that Cushing syndrome in dogs is highly unlikely, whereas a higher ratio than this amount would suggest the presence of the disease at some level in the dog.
Cost
The UCCR test is generally less expensive compared to other diagnostic tests for Cushing's disease, which makes it a cost-effective option for initial screening. Prices can vary, but they typically range from $50 to $100, depending on the veterinary clinic and location.
ACTH Stimulation Test
ACTH is a hormone produced in the pituitary gland that stimulates the adrenal glands to release another hormone called cortisol. The ACTH stimulation test for dogs measures how well the adrenal glands respond to adrenocorticotropic hormone (ACTH).
It is one of the primary blood tests for Cushing’s disease in dogs and is much more extensive compared to simpler screening tests. This is because it involves multiple steps, more time, resources, and handling, and it also provides more detailed information about the function of the adrenal glands.
The process begins by collecting a baseline blood sample from the dog to measure cortisol levels under normal, non-stimulated conditions. After the baseline sample is taken, the veterinarian injects synthetic adrenocorticotropic hormone (ACTH) directly into the dog to stimulate the adrenal glands to produce cortisol.
A second blood sample is drawn about an hour later to measure cortisol levels post-stimulation, after giving time for the ACTH to go into effect. Vets weigh up the ability of the adrenal glands to produce cortisol by measuring how much they have responded to ACTH.
Interpreting the Results
In a healthy dog, cortisol levels will rise within a normal range after ACTH is administered. Whereas, a significant increase in cortisol levels after stimulation would indicate the presence of pituitary-dependent Cushing's disease, which is characterized by overactive adrenal glands.
Conversely, if the adrenal glands fail to produce adequate cortisol, even after ACTH stimulation, it may be a sign of Addison’s disease, where cortisol levels remain abnormally low.
Although the ACTH stimulation test requires two blood draws and is crucial for diagnosing adrenal gland disorders, it does not distinguish between different types of Cushing’s disease. Therefore, additional diagnostic testing for Cushing’s disease in dogs is needed to determine the specific type and underlying cause of the disease.
Cost
The ACTH test for dogs is more expensive than the previously explained UCCR test. It can range from anywhere between $150 to $250, depending upon the location of the clinic and the expertise of the veterinarian.
Low-Dose Dexamethasone Suppression Test
The Low-Dose Dexamethasone Suppression Test (LDDST) is another crucial diagnostic dog Cushing’s test used to evaluate the function of the adrenal glands in dogs, diagnosing Cushing’s syndrome and determining its type.
The procedure begins with the collection of a baseline blood sample to measure cortisol levels under normal conditions. Following this, the veterinarian administers a low dose of dexamethasone, a synthetic steroid, which is intended to suppress cortisol production.
After administering the dexamethasone, additional blood samples are collected at specific intervals, typically 4 hours and 8 hours later, to assess how cortisol levels change in response to the suppression. In total, LDDST requires about 3 blood samples.
In most cases, the low-dose dexamethasone suppression test will complete the diagnosis of Cushing's disease and indicate the type of Cushing's disease (pituitary versus adrenal origin) present.
Low Dose Dexamethasone Suppression Test Interpretation
If the dog has a pituitary-origin Cushing's disease, there may be a slight decrease in cortisol levels at the four or eight-hour mark. Still, the reduction is often not substantial enough to fall within normal limits.
In contrast, with adrenal-origin Cushing's disease, there will typically be no significant reduction in cortisol concentrations at either the four or eight-hour intervals, as the adrenal tumor or hyperplasia continues to produce excessive cortisol despite the suppression attempt.
Cost
The cost of the LDDST test for dogs typically ranges between $150 to $250. Remember, prices can vary based on the veterinary clinic, location, and additional services included. But this cost generally covers the blood draws, the dexamethasone administration, and the analysis of cortisol levels at the lab.
Having said that, it’s always better to check with your veterinarian to learn about the latest test prices and to seek guidance about your dog’s health issues.
High-Dose Dexamethasone Suppression Test
This test works on the same principle as the low-dose test and is used when no reductions in cortisol levels are observed from the low-dose test. This test aims to determine which type of Cushing's disease is present in the dog.
The test also starts with the collection of a baseline blood sample to measure cortisol levels under normal conditions. Next, the dog is given a high dose of dexamethasone. After the administration, additional blood samples are taken at specific intervals, usually at 4 and 8 hours, to assess how cortisol levels respond to the high dose of dexamethasone.
Interpreting the Results
In cases of pituitary-dependent Cushing's disease, a significant suppression of cortisol production is observed, as the pituitary tumor's response to dexamethasone is often more variable.
However, in adrenal-dependent Cushing's disease, where the issue is with an adrenal tumor or hyperplasia, cortisol levels usually remain high, indicating that the adrenal glands are producing excess cortisol independently of the pituitary regulation.
These Cushing’s test results help the veterinarians distinguish between pituitary and adrenal forms of Cushing’s disease, and in guiding appropriate treatment strategies.
Cost
The cost of the High-Dose Dexamethasone Suppression Test (HDDST) for dogs is somewhere between $200 to $350. This is one of the most expensive types of invasive test for dogs and price fluctuations between different veterinary locations are expected.
Conclusion
Diagnosing Cushing's disease in dogs involves a range of tests, each providing valuable insights into adrenal gland function. Starting with the Urine Cortisol Ratio (UCCR) test for preliminary screening and moving to the ACTH Stimulation Test, Low-Dose Dexamethasone Suppression Test (LDDST), and High-Dose Dexamethasone Suppression Test (HDDST) for a more detailed assessment; each test plays a crucial role in confirming the presence and type of Cushing's disease.
In most cases, a combination of these tests will either confirm or rule out the possibility of Cushing's disease in your pet. While costs and procedures may vary, having a clear understanding of these tests will enable you to collaborate effectively with your veterinarian and ensure the best possible care for your furry friend.
FAQs
What are the Signs of Cushing's Disease in Dogs?
The most prevalent signs of Cushing's syndrome in dogs include increased thirst, lethargy, muscle weakness, and thin skin.
What are the Confirmatory Tests for Cushing's Syndrome?
The Endocrine Society's Clinical Practice Guidelines recommend dexamethasone suppression test, late-night salivary cortisol, and 24-hour urinary-free cortisol to confirm if your dog is suffering from Cushing’s syndrome or not.