Renin is an enzyme secreted by specialised cells (juxtaglomerular cells) in the kidneys in response to low blood pressure, low sodium, or reduced renal perfusion. Renin initiates the renin-angiotensin-aldosterone system (RAAS) — the key hormonal cascade that regulates blood pressure and sodium-potassium balance — by converting angiotensinogen to angiotensin I.
Renin testing is most commonly combined with aldosterone measurement as the aldosterone-to-renin ratio (ARR) — the primary screening test for primary hyperaldosteronism (Conn's syndrome), which causes hypertension, low potassium, and elevated aldosterone with suppressed renin. Renin is also measured in secondary hyperaldosteronism (where both renin and aldosterone are elevated) and in rare renin-secreting tumours.
FAQs
What is the aldosterone-to-renin ratio (ARR)?
The ARR is calculated by dividing the aldosterone level by the renin level. A high ratio (elevated aldosterone relative to suppressed renin) is the screening test for primary hyperaldosteronism. It is more specific than either measurement alone.
What is Conn's syndrome?
Conn's syndrome (primary hyperaldosteronism) is the most common secondary cause of hypertension, affecting approximately 5-10% of hypertensive patients. An adrenal adenoma produces excess aldosterone autonomously, suppressing renin. It causes hypertension, low potassium, and cardiovascular complications.
Should I stop my blood pressure medications before renin testing?
Ideally yes, under specialist guidance. Medications including beta-blockers, ACE inhibitors, ARBs, and diuretics all significantly affect renin and aldosterone results. A washout period of 2-4 weeks for most medications is recommended, though this must be done safely under medical supervision.
Can renovascular hypertension cause high renin?
Yes. Renal artery stenosis reduces blood flow to the kidney, stimulating renin release. This causes secondary hyperaldosteronism with both elevated renin and elevated aldosterone. Renal Doppler ultrasound or CT angiography can identify the stenosis.
