Low-Dose Dexamethasone Suppression Test (LDDST)
An 8-hour dynamic endocrine test that screens for Cushing’s disease and differentiates pituitary-dependent from adrenal-dependent forms.
💬 In Plain English
The LDDST is considered the screening test of choice for diagnosing Cushing’s disease in dogs. In a healthy animal, injecting a tiny dose of synthetic steroid (dexamethasone) tricks the brain into thinking the body has plenty of cortisol, shutting down ACTH production and suppressing blood cortisol levels for over 8 hours. In a dog with Cushing’s disease, the abnormal tumor ignores this feedback and continues churning out cortisol. By drawing blood at baseline, 4 hours, and 8 hours, the test not only confirms Cushing’s but can also distinguish between pituitary tumors and adrenal gland tumors.
🔬 Clinical & Technical Depth
For Vets & TechniciansFormal Clinical Definition
Dynamic pituitary-adrenal negative feedback test. Baseline cortisol is obtained (T0), dexamethasone sodium phosphate (0.01–0.015 mg/kg IV) is administered, and serum cortisol is measured at 4 hours (T4) and 8 hours (T8). Failure of suppression at 8 hours (>1.0–1.4 µg/dL) confirms hyperadrenocorticism.
Why Veterinarians Use It
Veterinarians prefer the LDDST for initial Cushing’s screening because of its superior diagnostic sensitivity (~90–95%) compared to the ACTH stimulation test.
Clinical Context Encountered
Performed as a day-stay hospital protocol where the dog remains quietly in the clinic for an 8-hour timeline.
Clinical Reference Guide (Diagnostic Test)
- •The LDDST should NOT be used if you suspect Addison’s disease: dexamethasone suppression is designed solely for hyperadrenocorticism, whereas ACTH stimulation is required for Addison’s.
❓ Questions to Ask Your Veterinarian
Take these actionable questions with you to your next clinic visit or appointment:
- 1Did the 8-hour cortisol result fail to suppress, confirming Cushing’s disease?
- 2Did the 4-hour cortisol show temporary suppression (<50% of baseline), confirming pituitary-dependent disease?
- 3If suppression did not occur at 4 hours, is an abdominal ultrasound recommended to look at the adrenal glands directly?
- 4Were any stressful hospital events present during the 8-hour stay that could trigger stress cortisol release?
Academic & Clinical References
- ACVIM Consensus Statement: Diagnosis of Spontaneous Canine HyperadrenocorticismOrganization: American College of Veterinary Internal Medicine (ACVIM) • Accessed: 2026-01-10https://www.acvim.org