Cortisol Testing: Cushing's & Addison's Disease Guide¶
Cortisol testing supports the diagnosis and monitoring of the two major canine adrenal disorders: Cushing's syndrome (hyperadrenocorticism) and Addison's disease (hypoadrenocorticism).
Why Cortisol Testing Is Dynamic¶
A single basal cortisol value is rarely diagnostic. Cortisol testing is dynamic — the response to stimulation or suppression is what carries the diagnosis.
Test Protocols¶
| Protocol | What it tests | Use |
|---|---|---|
| Basal cortisol | Resting level | Screening (limited alone) |
| ACTH stimulation | Adrenal response | Cushing's diagnosis + Addison's diagnosis + treatment monitoring |
| Low-dose dexamethasone suppression | Pituitary feedback | Cushing's diagnosis + differentiation |
Interpreting Results¶
Cushing's (Hyperadrenocorticism)¶
| Test | Finding |
|---|---|
| ACTH stim | Exaggerated cortisol response |
| LDDS | Failure to suppress cortisol |
Addison's (Hypoadrenocorticism)¶
| Test | Finding |
|---|---|
| ACTH stim | Blunted / absent cortisol response (diagnostic) |
Reference Ranges¶
| Analyte | Species | Basal Range |
|---|---|---|
| Cortisol (basal) | Canine | 2–6 µg/dL |
Clinical Context¶
- Cushing's: PU/PD, polyphagia, pot-belly, alopecia, elevated liver enzymes.
- Addison's: waxing/waning lethargy, GI signs, electrolyte abnormalities (Na/K ratio).
FAQ¶
Can I diagnose Cushing's with a single cortisol? No — a single basal cortisol is non-diagnostic. Dynamic testing (ACTH stim or LDDS) is required.
How is treatment monitored? ACTH stimulation pre- and post-trilostane dosing monitors adrenal suppression.
Case Study: The Polyuric Terrier¶
A 9-year-old Jack Russell Terrier presents with polyuria/polydipsia, polyphagia, and a pot-bellied appearance.
- Basal cortisol: 4.5 µg/dL (non-diagnostic alone).
- Low-dose dexamethasone suppression (LDDS): cortisol fails to suppress at 8 h — consistent with hyperadrenocorticism (Cushing's).
Management: Trilostane was initiated; ACTH stimulation pre- and post-dose is used to monitor adrenal suppression and titrate the dose.
Lesson: A single cortisol is never diagnostic — the dynamic response (suppression or stimulation) carries the diagnosis, which is why timed, same-day cortisol results are clinically essential.
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
For the review policy, see the Editorial & Review Policy.
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.