Renin

Overview

Renin is an enzyme secreted by the juxtaglomerular cells of the kidney that measures plasma activity or concentration as part of the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. It cleaves angiotensinogen to produce angiotensin I, leading to vasoconstriction and aldosterone release. Elevated levels indicate renovascular hypertension, malignant hypertension, or volume depletion, while low levels suggest primary aldosteronism or Cushing's syndrome; it is clinically useful for differentiating secondary hypertension causes and guiding medical management of endocrine hypertension.

Clinical Use Cases

  • Diagnosing primary aldosteronism (low renin, high aldosterone).
  • Evaluating renovascular hypertension (high renin).
  • Assessing hypokalemia with suspected mineralocorticoid excess.
  • Monitoring response to ACE inhibitors or ARBs.
  • Investigating resistant hypertension etiology.

Specimen Types

  • Plasma (EDTA tube, preferred).
  • Serum (less common).

Measurement Methods

  • Radioimmunoassay for plasma renin activity (PRA).
  • Immunometric assays for direct renin concentration.
  • Automated chemiluminescent immunoassays.

Test Preparation and Influencing Factors

  • Strict upright posture (2-4 hours ambulatory) before collection.
  • Liberal sodium diet (200-400 mEq/day) for 3 days prior.
  • Hold medications: ACE inhibitors, beta-blockers, diuretics for 2 weeks (physician approval).
  • Avoid estrogen therapy or licorice.
  • Time morning collection after overnight fast.

Synonyms

  • Plasma renin activity (PRA).
  • Direct renin concentration.
  • Renin mass.

Further Reading