Diagnosing Cushing’s Disease in Dogs
Any dog suspected of having hyperadrenocorticism will likely undergo a thorough physical examination and history, together with an initial database including a complete blood count (CBC), a serum biochemistry profile and a urinalysis, with or without a bacterial culture. Other fairly routine diagnostic tests include abdominal radiographs and/or ultrasound, and blood pressure assessment.
There are a number of more advanced laboratory tests available to help a veterinarian confirm a diagnosis of Cushing’s disease. These include a urine cortisol:creatinine ratio analysis, a low-dose dexamethasone suppression blood test, a high-dose dexamethasone suppression blood test, an ACTH stimulation blood test, and/or an assessment of endogenous blood ACTH concentrations. Magnetic resonance imaging (MRI) and computed tomography scans (CT or CAT scans) are also available to aid in the diagnostic process, as they may help visualize tumors of the pituitary or adrenal glands.
One of the simplest of these tests is the urine cortisol:creatinine ratio test. Normally, the owner is asked to catch the first morning’s urine at home and bring it to their veterinarian for measurement of cortisol and creatinine levels. Normal test results essentially rule out the diagnosis of Cushing’s. However, abnormal test results (called “false positives”) are common in up to 75% of dogs that do not have Cushing’s disease, making further diagnostic tests necessary.
The high- and low-dose dexamethasone suppression tests and the ACTH stimulation test, done together or separately, can lead to a conclusive diagnosis of Cushing’s disease. These tests involve first taking an initial blood sample, giving the dog an injection of either dexamethasone or ACTH, and then taking subsequent blood samples at appropriate intervals. All of the blood samples are sent to a laboratory for careful analysis. The dog’s veterinarian is in the best position to decide which tests to perform in any given case.
While Cushing’s can be frustrating for owners, it is usually possible to manage.