Interpret Captopril Challenge Test for PA

STEP 1 — Gather Information

• Measure baseline plasma aldosterone concentration (PAC) and plasma renin activity (PRA) after seated/standing ≥1h, ensuring medications that affect the ARR (ACEi, ARBs, diuretics, MR antagonists) have been withdrawn per guideline Table 5.
• Administer 25–50 mg captopril orally.
• Draw blood for PAC, PRA, and cortisol at 0 h and 1–2 h post‑dose, keeping the patient seated during the interval.

STEP 2 — Rule In / Rule Out

• If PAC decreases by ≥30% from baseline → PA unlikely (normal captopril response).
• If PAC decreases by <30% and PRA remains suppressed → proceed to further stratification (possible PA).
• If PAC decreases <30% but PRA is not suppressed → test indeterminate; consider alternative causes.

STEP 3 — Classify or Stratify

• Among non‑suppressed cases, assess degree of aldosterone change:
  • Some suppression (0 % < ΔPAC < 30 %) → favors idiopathic adrenal hyperplasia (IAH).
  • No suppression or rise (ΔPAC ≤ 0 %) → favors aldosterone‑producing adenoma (APA).

STEP 4 — Decide

• IAH‑suggestive pattern: consider saline infusion test or fludrocortisone suppression test for confirmation.
• APA‑suggestive pattern: proceed to adrenal venous sampling for lateralization and potential unilateral adrenalectomy.
• PA unlikely: investigate other causes of hypertension; do not pursue PA‑specific work‑up.

Clinical Guardrails / Mimics / Pitfalls

• Do not interpret CCT if patient is on ACE inhibitors, ARBs, potassium‑wasting/sparing diuretics, MR antagonists, or NSAIDs without adequate washout (see Table 5).
• Avoid in severe uncontrolled hypertension, hypokalemia, or congestive heart failure due to altered aldosterone dynamics.
• False‑negative/equivocal results occur in up to ~30 % of cases; a non‑suppressive CCT alone does not confirm PA.
• Ensure seated posture and adequate sodium intake; recumbent posture or sodium restriction can blunt the test response.

Concrete Clinical Example

A 58‑year‑old with resistant hypertension (BP 168/96 mm Hg) has baseline PAC 22 ng/dL, PRA 0.18 ng/mL/h. After 50 mg captopril, PAC falls to 16 ng/dL (27 % suppression) and PRA remains 0.09 ng/mL/h. Because suppression is <30 % and PRA stays suppressed, PA is suspected; subsequent AVS shows lateralization consistent with an aldosterone‑producing adenoma, leading to laparoscopic adrenalectomy.

Source: The Management of Primary Aldosteronism: Case Detection, Diagnosis, and Treatment: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2016, DOI:10.1210/jc.2015-4061