Determine when to perform dexamethasone suppression test for cortisol co-secretion
STEP 1 — Gather Information
Document adrenal tumor presence on CT (size, laterality) and assess for hypertension or hypokalemia.
Action: Record tumor size and proceed to size‑based decision.
STEP 2 — Rule In / Rule Out
Is an adrenal tumor identified on CT?
- Yes: Proceed to Step 3.
- No: Dexamethasone suppression test not indicated for cortisol co‑secretion evaluation.
STEP 3 — Classify or Stratify
Stratify by tumor size: >3.0 cm vs ≤3.0 cm.
Action: If tumor >3.0 cm, proceed to dexamethasone suppression test; if ≤3.0 cm, consider test based on additional clinical features (e.g., hypertension, hypokalemia).
STEP 4 — Decide
Administer 1 mg dexamethasone at night; measure serum cortisol the next morning between 8–9 am.
- Cortisol ≥1.8 μg/dL: Diagnose autonomous cortisol co‑secretion.
- Cortisol <1.8 μg/dL: No autonomous cortisol co‑secretion detected.
Clinical Guardrails / Mimics / Pitfalls
Do not test in patients receiving exogenous glucocorticoids; ensure proper dexamethasone dosing and timing; avoid false positives from acute stress or illness; test evaluates subclinical cortisol excess, not frank Cushing’s syndrome; interpret results in clinical context and coordinate peri‑operative stress‑dose glucocorticoids if surgery planned.
Concrete Clinical Example
A 60‑year‑old woman with hypertension and mild hypokalemia has an incidentally discovered 3.5 cm left adrenal nodule on CT; the clinician planning AVS asks about cortisol co‑secretion. A 1 mg overnight dexamethasone suppression test yields a morning cortisol of 2.4 μg/dL (≥1.8 μg/dL), indicating autonomous cortisol co‑secretion. She is referred for adrenalectomy with peri‑operative stress‑dose glucocorticoid coverage.
Source: Japan Endocrine Society clinical practice guideline for the diagnosis and management of primary aldosteronism 2021, Japan Endocrine Society, 2021