- 1). Test for dexamethasone suppression (DST). This is the most common and reliable test for equine Cushing's disease, but it does have a risk for false positives, according to Washington State University. This test requires two visits from the veterinarian.
- 2). Draw blood for a baseline test. The veterinarian will use this blood sample to compare cortisol levels in the second blood sample.
- 3). Inject dexamethasone into the muscle tissue. In healthy horses, dexamethasone acts on the pituitary gland to suppress the production of cortisol, a hormone. Most horses with Cushing's disease will not respond to dexamethasone due to the malfunctioning pituitary gland and will not show a decrease in cortisol levels, according to Penn State University.
- 4). Draw blood 20 hours after the dexamethasone injection. The veterinarian will send both of the blood samples to a lab to test the cortisol levels. Suppressed cortisol levels would indicate that the pituitary gland is functioning while unchanged cortisol levels may lead to a diagnosis of Cushing's disease.
- 5). Discuss other tests for Cushing's disease with your veterinarian. Additional tests for equine Cushing's disease include TRH-Response Test, which also tests cortisol levels, and the domperidone response test. These tests may be more expensive as they require additional veterinary visits.
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