Angiotensin II

The Angiotensin II test (plasma Ang II) is used to assess renin–angiotensin–aldosterone system activity during the workup of hypertension, abnormalities of sodium or fluid balance, and heart failure. Measurement may also aid evaluation of persistent angiotensin II activity despite angiotensin‑converting enzyme inhibitor therapy (ACE escape) described in a subset of patients with chronic heart failure.

Renin cleaves angiotensinogen to angiotensin I, which angiotensin‑converting enzyme converts to angiotensin II. Angiotensin II exerts potent vasoconstrictor effects, promotes aldosterone secretion, and enhances renal sodium reabsorption, leading to expansion of extracellular volume and an increase in arterial pressure. Circulating angiotensin II therefore reflects the downstream activity of the renin–angiotensin–aldosterone system. In heart failure, neurohormonal systems, including the renin–angiotensin–aldosterone cascade, may remain chronically activated. Some patients exhibit persistent angiotensin II activity during treatment with angiotensin‑converting enzyme inhibitors, a phenomenon termed ACE escape. In these contexts, plasma angiotensin II measurement can document ongoing renin–angiotensin activity and complement clinical assessment.