🧪 Aldosterone–Renin Ratio (ARR) is the key screening test for primary hyperaldosteronism (Conn’s syndrome), a potentially curable cause of hypertension. 💡 Excess aldosterone → sodium and water retention → hypertension, while renin is suppressed due to negative feedback.

📖 About

ARR is a screening test in hypertensive patients at risk of primary hyperaldosteronism.
Interpreted in context of renin and aldosterone levels.
Renin–aldosterone axis is regulated by renal perfusion, sodium intake, and potassium balance.
Patients should be euvolaemic, on a normal diet with adequate sodium intake, and have corrected potassium before testing.
Routine clotting/platelet checks are not required before testing.

🎯 Indications

Hypertension with unexplained or refractory hypokalaemia.
Resistant hypertension (≥3 antihypertensives ineffective).
Severe hypertension (SBP >160 or DBP >100 mmHg).
Hypertension with adrenal incidentaloma.
Young age of onset hypertension or family history of early stroke/Conn’s.

🧪 Plasma Renin Activity (PRA)

Sometimes measured alone (e.g. Addison’s disease, CAH) to monitor adequacy of mineralocorticoid replacement.
In Conn’s, renin is characteristically suppressed.

📊 Normal Values

Aldosterone: ≤ 630 pmol/L (upright, adults).
Renin (recumbent): 1.1–2.7 pmol/mL/h.
Renin (upright): 2.8–4.5 pmol/mL/h.
Random sample: 0.5–3.5 pmol/mL/h.

⚠️ Preparation

Medications: Stop spironolactone, eplerenone, amiloride, and triamterene ≥6 weeks before test if safe. Other antihypertensives (ACEi, ARBs, diuretics, beta-blockers, CCBs) may interfere and should ideally be stopped, but only if clinically safe. Substitute with doxazosin, verapamil, or hydralazine if BP control needed.
Potassium: Correct hypokalaemia before test (low K⁺ suppresses aldosterone).
Sodium intake: Normal diet, avoid restriction or excessive intake.
Posture: Seated for 30 mins prior to venepuncture (standardisation reduces false results).
Sample handling: Blood in EDTA tube, kept at room temp (do not chill, as renin cryoactivates). Send immediately to lab.

🧾 Sample Requirements

Adults: 4 mL venous blood in EDTA tube.
Notify lab in advance if ARR is being performed.

📈 Interpretation

ARR >35 with aldosterone >300 pmol/L → highly suggestive of primary hyperaldosteronism (Conn’s syndrome). Sensitivity ~100%, specificity ~90%.
False negatives: ongoing ACEi/ARB/diuretics, low sodium intake, hypokalaemia.
False positives: beta-blockers (suppress renin), poor posture control.

🔎 Next Steps if ARR Positive

Confirm with suppression test (saline infusion test, oral sodium loading, fludrocortisone suppression test).
Adrenal imaging (CT) to assess for adenoma vs hyperplasia.
Adrenal vein sampling (gold standard) if surgical treatment considered.

💡 Clinical Pearl: ARR is a screening test only. Always confirm with suppression testing before labelling as Conn’s syndrome. Early recognition is vital - surgical cure is possible in unilateral adenoma, while bilateral hyperplasia is treated medically with mineralocorticoid antagonists.

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Renin and Aldosterone Renin ratio (ARR)