Very Common
Less Common
Related Observations
Your vet might choose this diagnostic test if you were making these observations.
Diagnostic
Tests or procedures used by your vet to determine what is wrong with your horse, in order to reach a diagnosis.
Cost: $100 to $500
These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.
YOUR VET MAY PERFORM
Dexamethasone Suppression Test, DST
Cost: $100 to $500
These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.
Summary
This test is used to confirm or rule out the presence of Pituitary Pars Intermedia Dysfunction (PPID, Cushing's Disease). It is used by some vets instead of or in addition to the Endogenous ACTH test.
A blood sample is taken from the horse and the cortisol (a normal steroid hormone produced by the adrenal glands) is measured. Then, dexamethasone (a potent steroid) is injected into the horse. After 19 hours, another blood sample is taken from the horse and the cortisol level is measured again.
In a normal horse, the body responds to the shot of dexamethasone by shutting down the production of its own steroids, including cortisol. In horses with PPID this steroid reduction does not take place, and the second blood sample contains the relatively same amount of cortisol as the first.
A blood sample is taken from the horse and the cortisol (a normal steroid hormone produced by the adrenal glands) is measured. Then, dexamethasone (a potent steroid) is injected into the horse. After 19 hours, another blood sample is taken from the horse and the cortisol level is measured again.
In a normal horse, the body responds to the shot of dexamethasone by shutting down the production of its own steroids, including cortisol. In horses with PPID this steroid reduction does not take place, and the second blood sample contains the relatively same amount of cortisol as the first.
Why A Vet Chooses This Diagnostic
Related Diagnostics
Other diagnostic tests that might be used in combination or with this one or instead of this one.
Diagnoses Your Vet May Consider
This test could rule out or confirm any of the following diagnoses.
BENEFITS
This test may be somewhat more reliable year-round than the endogenous ACTH test, and the cost is comparable. The reliability of this test is well documented, and compares favorably to Endogenous ACTH. LIMITATIONS
This test requires drawing two blood samples taken 19 hours apart, which is inconvenient. Like endogenous ACTH, the reliability of the result decreases in the fall in the Northern Hemisphere because of seasonal variation in normal responses.
Personally, I am reluctant to give horses dexamethasone if they have or have had a history of laminitis. Steroids can cause or worsen laminitis. While this dose of steroids is minimal and unlikely to cause a problem in an otherwise healthy horse, there is a possibility it could worsen laminitis in a horse already predisposed.
your role
Questions To Ask Your Vet:
- Why use this test over simply taking a blood sample for endogenous ACTH?