Cushing’s disease seems to be on every veterinarian’s mind these days. Because of this, many screening tests are recommended to diagnose Cushing’s disease. These tests are relatively reliable if there are signs and symptoms as well as lab abnormalities.
But what if these same tests are used on animals that aren’t showing these signs and symptoms? False positive results can occur.
In addition, these tests are done at the veterinary hospital. That has impacts too. The dog is caged and the stress of hospitalization alone may cause a false positive result. Even the suggestion that a dog will wind up at the vet is enough to start the dog’s adrenals working overtime.
Because of its sensitivity, many vets consider the Low Dose Dexamethasone Suppression Test the best option. The problem with this test is it gives too many false positive results. As I said before, the stress the dog is undergoing will have a definite influence on the test results. Being locked in a cage and having blood drawn is definitely enough stress to create a false positive.
Another test, the ACTH Stimulation Test, is a popular screening test. I can’t tell you why. In general, this kind of test would be used for hypofunction, not hyperfunction, of the adrenal glands. This test misses many animals that have the disorder. I’m talking typically 20% to 30% of dogs with pituitary abnormality and 50% with an adrenal tumor.
These tests should only be used when the animal has the clinical signs of the disease. These are all the signs I mentioned above that Spot didn’t have.
There’s an excellent test you can do on your dog’s urine called a Cortisol-Creatinine Ratio Test. This test is very useful for ruling out Cushing’s disease; it has an accuracy rate of 90%. The urine has to be taken at home and the dog can’t be stressed out. Don’t even let him know that he might be going to the veterinarian’s office later on that day!
When you bring the urine sample for testing, ask the veterinarian to do a urine specific gravity. A urine specific gravity of less than 1.025 is consistent with Cushing’s disease. Dogs with a urine specific gravity greater than 1.025 are less likely to have Cushing’s.
By far, the most accurate, safe and effective method of diagnosing Cushing’s disease is the Cortisol Creatinine Ratio on an unstressed urine followed by an ultrasound.
So let’s look at this scenario. Spot has none of the signs and symptoms of Cushing’s disease. He has a high alkaline phosphatase. His cortisol creatinine ratio is elevated. What do you do? The best thing to do is find a specialty clinic that has a radiologist who does ultrasounds. Ask for a full abdominal ultrasound and have the doctor check and size both adrenals. If they’re normal in size, and your dog has none of the symptoms, it’s very likely your dog doesn’t have Cushing’s disease.