What Is Renin?
Renin is an enzyme released by the kidneys in response to low blood pressure or low sodium. It triggers the renin-angiotensin-aldosterone system (RAAS) — a cascade that raises blood pressure by retaining sodium and water.
Normal Plasma Renin Activity
| Position | Normal Range |
|---|---|
| Seated (after 1–2 hours upright) | 0.6–4.3 ng/mL/hr |
| Supine (lying for 30 min) | 0.2–1.6 ng/mL/hr |
| Sodium-depleted (stimulated) | 2.9–24 ng/mL/hr |
Aldosterone-to-Renin Ratio (ARR)
The ARR is the key diagnostic tool for primary hyperaldosteronism. A high ARR (above 20–30, depending on lab units) with a high aldosterone level suggests autonomous aldosterone production.
High Renin Causes
- Renovascular hypertension (renal artery stenosis)
- Secondary hyperaldosteronism (heart failure, cirrhosis, nephrotic syndrome)
- Low blood volume (dehydration, haemorrhage)
- Renin-secreting tumours (juxtaglomerular tumours — rare)
Low Renin Causes
- Primary hyperaldosteronism (Conn's syndrome) — high aldosterone suppresses renin
- Excess salt intake
- Cushing's syndrome
FAQs
How should I prepare for a renin test?
Posture matters — results differ from lying vs. sitting. Your doctor will specify. Certain medications must be paused for 2–4 weeks.
Is renin testing routine?
No — it's specifically ordered to investigate resistant hypertension or a suspected aldosterone-renin imbalance.
What is renovascular hypertension?
Narrowing of the arteries supplying the kidneys triggers high renin release, causing hard-to-treat high blood pressure — often improved by correcting the artery blockage.
Medical Disclaimer: Renin testing requires specific preparation and must be interpreted alongside aldosterone and clinical history by a specialist.