Aldosterone-to-Renin Ratio (ARR)

The Aldosterone-to-Renin Ratio (ARR), also known as the aldosterone–renin ratio, is used as a first-line screen for primary aldosteronism. The result helps distinguish autonomous aldosterone production from renin-driven processes and supports the differential diagnosis of secondary hypertension. ARR testing is appropriate when evaluating resistant or severe hypertension, hypertension accompanied by hypokalemia, and hypertension in the setting of an adrenal incidentaloma. Results guide further confirmatory testing and subsequent subtype evaluation when primary hyperaldosteronism is suspected.

Aldosterone is a mineralocorticoid synthesized in the adrenal cortex that maintains sodium retention and potassium excretion. Secretion is principally governed by the renin–angiotensin system: reduced renal perfusion or decreased distal tubular sodium delivery stimulates renin, angiotensin II forms, and angiotensin II drives aldosterone release. Physiologic output shows an early-morning peak and varies with sodium and potassium balance, posture, pregnancy, smoking, physical activity, stress, and medications that modify renin or aldosterone. Primary hyperaldosteronism reflects autonomous aldosterone production—most often from an adrenal adenoma or bilateral hyperplasia—leading to sodium retention, potassium wasting, and hypertension. In this setting, the aldosterone-to-renin ratio is typically elevated because aldosterone is increased while renin is suppressed. Accurate ARR interpretation requires standardized collection conditions and careful review of factors that can alter either hormone, including body position, electrolyte status, and drug exposures.