Introduction
Signs of Cushing’s disease, or Hyperadrenocorticism, in dogs often mimic other diseases, and an accurate diagnosis involves a lot of detective work. Initial blood and urinalysis tests will help to increase or decrease the index of suspicion of Cushing’s and identify potential common and concurrent problems.
Testing for Cushing’s Disease
Any dog that your veterinarian suspects of having Cushing’s Disease should have an initial database of a complete blood count (CBC), a serum biochemistry profile and a urinalysis with a bacterial culture. Other fairly routine diagnostic tests might include abdominal and thoracic (chest) radiographs or ultrasound, and blood pressure assessment.
Advanced testing to confirm a diagnosis of Cushing’s disease 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 (CT) are also available to aid in diagnosis.
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. A normal test result pretty much rules 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 and ACTH blood tests, done together or separately, can provide a conclusive diagnosis of Cushing’s disease. These tests involve taking an initial blood sample, then giving the dog an injection of either dexamethasone or ACTH, then taking subsequent blood samples at appropriate intervals. All of the blood samples are sent to a laboratory for analysis. Your veterinarian will decide which test is best in a given case.