Has your veterinarian recommended the ACTH stimulation test for your dog? The ACTH stimulation test in dogs helps your veterinarian determine how the adrenal glands are functioning. These glands produce cortisol, a stress hormone important for many bodily processes. The test works by mimicking your dog's natural hormone production process and measuring the adrenal gland's response. This helps diagnose conditions like Cushing's disease (too much cortisol) or Addison's disease (too little cortisol).

What is the ACTH stimulation test in dogs?

Your dog's body has a complex communication system for managing hormones. The ACTH stimulation test taps into that system to understand how the adrenal glands are functioning. These tiny organs near the kidneys produce cortisol, a hormone that plays a key role in stress response, energy regulation, and immune function.

The ACTH stimulation test in dogs plays an important role in helping us diagnose both Cushing's disease (too much cortisol) and Addison's disease (too little cortisol).

The brain produces a hormone called ACTH (Adrenocorticotropic Hormone) that signals the adrenal glands to make cortisol. The ACTH stimulation test uses a synthetic version of ACTH to see if your dog's adrenal glands are responding appropriately.

How does the ACTH stimulation test work?

First, we will measure your dog's baseline cortisol level with a blood sample. Then, we'll inject the synthetic ACTH and take another blood sample 1-2 hours later to see how the cortisol level changes. The comparison of these two values is what helps us determine if your dog's adrenal glands are functioning properly.

How does the ACTH stimulation test help diagnose Cushing's or Addison's disease?

The ACTH stimulation test provides clues about how your dog's adrenal glands are responding to signals from the brain. Here's how those clues point towards specific diagnoses:

Healthy, normal adrenal response: If your dog has healthy adrenal glands, their cortisol levels should rise significantly after the ACTH injection. This indicates that the adrenal glands are functioning properly.

Cushing's disease: In dogs with Cushing's disease, the adrenal glands are already overproducing cortisol. The ACTH stimulation test may show an exaggerated increase in cortisol levels, or the cortisol may not change much because the glands are already working on overdrive.

Addison's disease: In dogs with Addison's disease, the adrenal glands are unable to produce enough cortisol, even with stimulation. The ACTH stimulation test will show little to no increase in cortisol levels, indicating an adrenal gland problem.

What are the limitations of the ACTH stimulation test?

While the ACTH stimulation test is a helpful tool, it's important to understand it has some limitations. Here's what you should keep in mind:

  1. Medication interference: Corticosteroids, such as prednisone, suppress cortisol production. If your dog has been taking corticosteroids, you'll need to discuss with your veterinarian how and when to safely discontinue their use before the test. Injectable dexamethasone can affect results for up to 7 days, and long-term use of some topical medications (eye, ear, or skin) can also influence the test.
  2. The impact of illness and stress: Conditions that cause chronic stress in your dog can lead to elevated cortisol levels, potentially affecting test results. In some cases, dogs with other illnesses may show a false positive for Cushing's disease on the ACTH stimulation test. Dogs with Addison's disease, however, will still have a low ACTH stimulation result.
  3. Potential for error: Laboratory errors, such as samples collected at the wrong time, can impact the accuracy of the test results. Additionally, the type of ACTH used in the test matters. Compounded ACTH products may have less supporting evidence than commercially available products, which could potentially influence the results.
  4. Not always conclusive: Even with a normal ACTH stimulation test result, Cushing's disease cannot be entirely ruled out, especially if your dog's symptoms and other laboratory findings strongly suggest it. In some cases, dogs with Cushing's disease can have normal test results.

Using the ACTH stimulation test to monitor the effectiveness of trilostane

Trilostane is a common medication used to treat Cushing's disease in dogs. Regular ACTH stimulation tests are important for monitoring how well your dog is responding to this medication and ensuring they are getting the appropriate dosage.

For accurate results, the ACTH stimulation test should be performed 2-6 hours after your dog has taken their trilostane medication along with a full meal.

Choose a specific timeframe within that 2-6 hour window (for example, always 4 hours after their pill) and stick to that same timing for all subsequent ACTH stimulation tests. This ensures consistent results and helps your veterinarian accurately track your dog's progress.

Monitoring trilostane effectiveness with the ACTH stimulation test helps your veterinarian fine-tune the dosage if needed. This optimizes control of Cushing's disease symptoms while minimizing the risk of side effects from over-suppressing the adrenal glands.

Vet's Tip: Your veterinarian will provide specific instructions on when and how to perform the ACTH stimulation test for monitoring purposes. They'll interpret the results in conjunction with how well your dog is doing and determine if any adjustments to the trilostane dose are needed.

The ACTH stimulation test plays an important role when it comes to assessing your dog's adrenal gland function. While the test has some limitations, it's a powerful tool when used in combination with your dog's overall health assessment. If your veterinarian recommends this test, remember that they're seeking the best way to understand your dog's condition. Early diagnosis and appropriate treatment are key for managing Cushing's disease or Addison's disease, helping your dog live a longer and healthier life.

If you have any questions or concerns about your dog, please contact your veterinarian.