Renin activity, plasma (PRA)
Salt-depleted, upright: 3.0–15 ng/mL/hr
Salt-replete, upright: 0.6–3.0 ng/mL/hr
The renal juxtaglomerular apparatus generates renin, an enzyme that converts angiotensinogen to angiotensin I. Renin secretion by the kidney is stimulated by a decrease in glomerular blood pressure, decreased sodium at the renal distal tubule, or renal vascular disease.
The inactive angiotensin I is then converted to angiotensin II, which is a potent vasopressor.
Renin activity is measured by the ability of a patient’s plasma to generate angiotensin I from substrate (angiotensinogen), and expressed as ng/mL/hr.
Normal values depend on the patient’s hydration, posture, and salt intake.
Increased in: Dehydration, some hypertensive states (eg, renal artery stenosis), edematous states (cirrhosis, nephrotic syndrome, heart failure), hypokalemic states (gastrointestinal sodium and potassium loss, Bartter syndrome), adrenal insufficiency, chronic renal failure, left ventricular hypertrophy. Drugs: ACE inhibitors, estrogen, hydralazine, nifedipine, minoxidil, oral contraceptives.
Decreased in: Hyporeninemic hypoaldosteronism, some hypertensive states (eg, primary aldosteronism, severe preeclampsia). Drugs: β-blockers, aspirin, clonidine, prazosin, reserpine, methyldopa, indomethacin.
An elevated ratio of plasma aldosterone concentration (in ng/dL) to plasma renin activity (aldosterone-to-renin ratio or ARR) of 20 or higher is an effective screening test for primary aldosteronism (sensitivity, 95%). It has a high negative predictive value even during antihypertensive therapy. Because of a low specificity of the ratio, autonomous aldosterone production must be confirmed by demonstration of high and autonomous secretion of aldosterone (using an aldosterone suppression test). The ARR should be interpreted along with the actual values of aldosterone and plasma renin activity.
Plasma renin activity is also useful in evaluation of hypoaldosteronism (low-sodium diet, patient standing) (see Aldosterone, serum).
Weiner ID. Endocrine and hypertensive disorders of potassium regulation: primary aldosteronism. Semin Nephrol 2013;33:265. [PMID: 23953804]
Zennaro MC et al. An update on novel mechanisms of primary aldosteronism. J Endocrinol 2015;224:R63. [PMID: 25424518]