Interpret Oral Sodium Loading Test for PA
STEP 1 — Gather Information
Collect 24‑hour urinary aldosterone excretion (g/24h) after 3 days of oral sodium loading (~200 mmol Na⁺/day). Verify adequate slow‑release potassium supplementation, absence of severe uncontrolled hypertension, renal insufficiency, cardiac arrhythmia, or severe hypokalemia, and confirm proper urine collection timing (morning of day 3 to morning of day 4).
STEP 2 — Rule In / Rule Out
Is urinary aldosterone excretion ≤10 g/24h?
- Yes → PA is unlikely (proceed to Step 4 – Decide: rule out PA).
- No → proceed to Step 3.
STEP 3 — Classify or Stratify
Is excretion ≥12 g/24h (Mayo Clinic) or ≥14 g/24h (Cleveland Clinic)?
- Yes → PA is highly likely.
- No (10 g/24h < excretion < cutoff) → indeterminate range; consider alternative confirmatory testing.
STEP 4 — Decide
- If PA unlikely: explore other causes of hypertension; avoid unnecessary adrenal work‑up.
- If PA highly likely: advance to subtype classification (adrenal CT, then AVS if indicated).
- If indeterminate: repeat the oral sodium loading test or perform another confirmatory test (e.g., saline infusion test, fludrocortisone suppression test).
Clinical Guardrails / Mimics / Pitfalls
Do not perform the test in patients with severe uncontrolled hypertension, renal insufficiency, cardiac arrhythmia, or severe hypokalemia. Ensure potassium supplementation to prevent hypokalemia‑induced false‑low aldosterone. Beware of renal metabolites (e.g., aldosterone‑18‑oxo‑glucuronide) that may blunt assay accuracy; use HPLC‑tandem mass spectrometry when available. Avoid testing in pregnancy. Inadequate 24‑h urine collection invalidates results.
Concrete Clinical Example
A 48‑year‑old woman with resistant hypertension and spontaneous hypokalemia undergoes oral sodium loading; her 24‑h urinary aldosterone excretion is 8 g/24h. Because this is ≤10 g/24h, PA is deemed unlikely, and the clinician investigates other secondary hypertension causes rather than pursuing adrenal venous sampling.
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