Determine When to Test for Germline KCNJ5 Mutations (FH-III)
STEP 1 — Gather Information
Confirm PA via elevated ARR and a positive confirmatory test (e.g., saline infusion, fludrocortisone suppression). Collect age, age of hypertension onset, serum potassium, and family history of PA or early stroke (<40 years).
STEP 2 — Rule In / Rule Out
Is the patient <20 years of age with confirmed PA? If yes, proceed to Step 3; if no, do not pursue germline KCNJ5 testing (consider FH-I/FH-II based on family history or routine workup).
STEP 3 — Classify or Stratify
Among patients <20 years with PA, assess for severe early-onset hypertension (SBP >160 mmHg or DBP >100 mmHg) and hypokalemia (serum K+ <3.5 mmol/L). If both are present, classify as high suspicion for FH-III; otherwise, classify as lower suspicion.
STEP 4 — Decide
If high suspicion, suggest germline KCNJ5 testing; if low suspicion, consider alternative diagnoses or proceed with FH-I/FH-II testing based on family history.
Clinical Guardrails / Mimics / Pitfalls
Do not test for germline KCNJ5 in patients >20 years without family history; avoid confusing germline KCNJ5 mutations with somatic KCNJ5 mutations in adenomas; ensure PA is confirmed before genetic testing; refrain from testing in patients with known FH-I or FH-II.
Concrete Clinical Example
A 6‑year‑old boy presents with hypertension 180/110 mmHg, hypokalemia K+ 2.9 mmol/L, elevated ARR, and positive saline suppression test; no family history. He is <20 years with confirmed PA and severe early‑onset hypertension with hypokalemia, prompting germline KCNJ5 testing.
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