Cortisol Dynamic Testing: ACTH Stimulation & Dexamethasone Suppression¶
A single basal cortisol is rarely diagnostic. Adrenal disease diagnosis relies on dynamic testing — measuring the cortisol response to stimulation or suppression. This page explains the two core protocols.
Why Dynamic, Not Basal¶
Cortisol fluctuates with stress, time of day, and disease. A single value is a snapshot; the response to a challenge reveals adrenal function:
| Protocol | Challenge | Diagnoses |
|---|---|---|
| ACTH stimulation | Synthetic ACTH → measure cortisol response | Addison's + Cushing's + treatment monitoring |
| Low-dose dexamethasone suppression (LDDS) | Dexamethasone → measure suppression | Cushing's + differentiation |
ACTH Stimulation¶
- Measure basal cortisol.
- Administer synthetic ACTH.
- Measure cortisol at 1 h (post-stimulation).
| Response | Interpretation |
|---|---|
| Exaggerated (high post) | Cushing's (hyperadrenocorticism) |
| Blunted/absent (low post) | Addison's (hypoadrenocorticism) — diagnostic |
Low-Dose Dexamethasone Suppression (LDDS)¶
- Measure basal cortisol.
- Administer dexamethasone.
- Measure cortisol at 4 h and 8 h.
| Response | Interpretation |
|---|---|
| Fails to suppress (8 h) | Cushing's |
| Suppresses normally | Rules out Cushing's |
References¶
- Van Liew CH, Greco DS, Salman MD. Comparison of results of adrenocorticotropic hormone stimulation and low-dose dexamethasone suppression tests with necropsy findings in dogs: 81 cases (1985-1995). J Am Vet Med Assoc. 1997;211(3):322-325. PMID: 9262671
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Authored by: Migibio Clinical & Scientific Affairs, Guangzhou Magic Biotech Co., Ltd.
Reviewed by: Migibio R&D Quality Committee
Last updated: 2026-08-13
Disclosure: Migibio (Guangzhou Magic Biotech Co., Ltd.) is the manufacturer of the FIA680/FIA880 analyzers and FICT reagents referenced in this content. See our Editorial & Review Policy.
Contact: Martin.Wong · Phone (WhatsApp): +86 13323237275 · Email: martinwang2024@gmail.com