Renin
Also called: Plasma renin activity, PRA, Direct renin
The kidney enzyme that starts the hormone cascade controlling blood pressure and salt balance. Measured with aldosterone, it is the test that uncovers primary aldosteronism — the commonest curable cause of high blood pressure.
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What does Renin measure?
Renin is released by the kidney when it senses low blood pressure, low salt or reduced blood flow. It launches the renin–angiotensin–aldosterone system (RAAS): renin leads to angiotensin, which raises blood pressure and triggers the adrenal glands to release aldosterone, which makes the kidney hold onto sodium and water. Because renin and aldosterone normally move together, the most useful reading is the pair — the aldosterone-to-renin ratio. When the adrenal makes aldosterone on its own (primary aldosteronism), the body suppresses renin, so a high aldosterone with a low renin is the tell-tale pattern. A high renin with high aldosterone instead points to the kidney or its blood supply driving the system (secondary). Renin is very sensitive to posture, salt intake and many blood-pressure drugs, so testing conditions must be controlled.
What does a high Renin level mean?
- Secondary hyperaldosteronism — the kidney drives the system: renal artery narrowing, heart failure, cirrhosis, dehydration.
- Diuretics and several blood-pressure medicines — raise renin (and can confound testing).
- Salt loss / low-sodium states, Addison's disease.
- Normal upright, low-salt physiology — renin rises appropriately.
What does a low Renin level mean?
- Primary aldosteronism (Conn's) — with a high aldosterone; the classic curable-hypertension pattern.
- High salt intake.
- Some low-renin forms of hypertension, certain adrenal enzyme conditions.
- Medications — beta-blockers and others lower renin.
When to discuss with a doctor
Renin is not a stand-alone test — it is half of the aldosterone-to-renin ratio used to screen for primary aldosteronism in people with high blood pressure that is resistant, early-onset, or comes with a low potassium. Because posture, salt and many antihypertensives shift renin, the test should be done under the conditions your doctor specifies, sometimes after adjusting medication. A suppressed renin with a raised aldosterone is the signal that goes to endocrinology for confirmation. Mediora.AI shows renin together with aldosterone and potassium so the ratio and pattern can be read; the interpretation and any medication adjustments belong with your doctor.