ACTH Stim Test for Dogs
- EverPal
- Aug 8, 2024
- 4 min read
Updated: Aug 9, 2024
Reviewed by Dr. Terry White, DVM
As a dog parent, hearing that your pet might have Cushing's syndrome can be overwhelming and confusing. The uncertainty and worry about your dog's health can be stressful. One of the most crucial steps in diagnosing this condition is the ACTH stimulation (ACTH stim) test.
Through this blog, we will help you understand the ACTH stim test for dogs, its purpose, procedure, and what to expect, so you can make informed decisions about your fur baby's health.
What is Cushing's Disease?
Cushing's disease, or hyperadrenocorticism, is a condition where the adrenal glands produce too much cortisol. This hormone is vital for various bodily functions, but in excess, it can lead to serious health problems.
Symptoms of Cushing's disease include increased thirst and urination, excessive hunger, panting, a pot-bellied appearance, hair loss, and lethargy.
The ACTH Stim Test for Dogs
The ACTH stim test is designed to assess the adrenal glands' ability to produce cortisol. It helps diagnose conditions like Cushing's disease and Addison's disease.
This test helps differentiate between normal and excessive cortisol production. In dogs with Cushing's disease, the adrenal glands release an abnormally high amount of cortisol in response to ACTH.
Why Your Dog Might Need an ACTH Stim Test
The ACTH stim test is crucial for several reasons:
Diagnosis: It helps confirm Cushing's disease, especially if your dog shows clinical signs and has abnormal blood tests.
Monitoring: The test is essential for monitoring dogs undergoing treatment for Cushing's disease to ensure that the medication is effectively controlling cortisol levels.
Steroid Medication: It is the only test suitable if Cushing's disease is suspected due to prolonged steroid medication use, as other tests might not work in such cases.
What to Expect During the ACTH Stim Test for Dogs
The test usually requires one to two hours. Here is how it works.
Preparation: Your dog should ideally be fasted overnight, and the test is usually performed in the morning between 8 a.m. and 10 a.m. to ensure consistent results.
Baseline Measurement: A blood sample is taken to measure the baseline cortisol level.
ACTH Administration: A synthetic form of adrenocorticotropic hormone (ACTH) is injected. This hormone stimulates the adrenal glands to release cortisol.
Second Measurement: After 1-2 hours, a second blood sample is taken to measure the cortisol level again.
Interpreting ACTH Stim Test Results
Understanding the results of an ACTH stim test can be challenging. Here's a simplified explanation:
Normal Response: If cortisol levels rise moderately after ACTH injection, it indicates normal adrenal function.
Excessive Response: A significant increase in cortisol levels suggests Cushing's disease.
Minimal Response: If there's little to no increase in cortisol levels, it might indicate Addison's disease or another adrenal insufficiency.
The Low Dose Dexamethasone Suppression Test
Other diagnostic tests for Cushing's disease include the low dose dexamethasone suppression (LDDS) test and the urine cortisol/creatinine ratio test.
Low Dose Dexamethasone Suppression Test for Dogs
The low dose dexamethasone suppression test for dogs helps classify the type of Cushing's disease but requires a longer hospital stay (at least 8 hours).
Dexamethasone is a cortisone hormone used for many treatments. When a dog gets dexamethasone, the pituitary gland detects it and stops telling the adrenal glands to produce steroids. In a healthy dog, blood cortisol levels drop 8 hours after a small dose of dexamethasone is given through a vein.
Test Accuracy
The low dose dexamethasone suppression test is the most accurate way to confirm Cushing's disease. About 90 percent of dogs with Cushing's disease will test positive with it.
What to Expect During the Test
Baseline cortisol is measured, followed by an intravenous dexamethasone injection, with subsequent blood samples taken at intervals over 8 hours.
The ACTH Stim Test vs. Low Dose Dexamethasone Supression Test
The LDDS test is better at detecting Cushing's disease. However, the ACTH stim test is more accurate and important for monitoring treatment. The LDDS test won't work if medications have already affected the dog's system.
The downside of the ACTH stim test is that it's not very sensitive. Because of this, the University of California Veterinary School no longer recommends it for diagnosing Cushing's disease in dogs.
The Urine Cortisol/Creatinine Ratio
This is a screening test for Cushing's disease. A negative result rules out Cushing's disease, but a positive result requires further testing.
Here is how this test works. A single urine sample is analyzed for cortisol and creatinine levels. If there is a high ratio, we would then conduct further testing. This test is best done at home to avoid stress from a vet visit, which can affect cortisol levels and interfere with the results.
Costs and Accessibility of the ACTH Stim Test
The cost of an ACTH stim test can vary, typically ranging from $150 to $300. Pet insurance might cover this test, so it's worth checking your policy. Most veterinary clinics can perform the ACTH stim test, but in some cases, a referral to a specialist might be necessary.
Addressing Common Concerns
Side Effects
The ACTH stim test is generally safe, but some dogs might experience temporary discomfort at the injection site. Serious side effects are rare.
Stress Management
Stress can affect cortisol levels, so try to keep your dog calm before and during the test. Collecting urine samples at home for the cortisol/creatinine ratio test can help minimize stress-related inaccuracies.
The ACTH stim test is a vital tool in diagnosing and managing Cushing's disease in dogs. By understanding its purpose, procedure, and what to expect, you can alleviate some of the anxiety and make informed decisions about your pet's care.
Are You Seeing Your Dog Having Increased Thirst and Urination, Hungrier, or Hair Loss?
We can help! EverPal's Medical Director, Dr. Terry White, brings 40 years of experience and is ready to meet your fur baby same-day for any concerns about your dog's health. Each visit is twice as long as your typical in-office visit, allowing our veterinarian to understand your dog's unique needs, explain multiple treatment options, and provide thorough guidance on the treament plan.
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