Makindo Medical Notes

Related Subjects: |Ferritin |CEA |ESR |CRP |ALP |LDH |HbA1c |Alpha Fetoprotein |Anti-Hu ab |Biochemical Lab values |Adrenal Physiology |Primary hyperaldosteronism (Conn's syndrome)

🧪 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.