Plasma renin activity (PRA) Renin is a protein hydrolase that is produced, stored, and secreted primarily by parabellular cells. Angiotensinogen produces angiotensin I (AngI) in response to renin. PRA is the rate of Ang-I production per unit time from renin action on angiotensinogen. Clinical significance: PRA measurement is of great value for renin typing of primary hypertension and screening diagnosis of secondary hypertension. the level of PRA is an important clue to suggest and detect secondary hypertension. Since there are three types of primary hypertension itself: low renin, orthorenin and high renin, the PRA test results alone are not sufficient to diagnose primary or secondary hypertension, and relevant biochemical and special tests are needed to provide complete information for differential diagnosis. 1, PRA decrease: there are primary hyporenal hypertension and secondary hyporenal hypertension. Studies have shown that 1/4-1/3 of patients with primary hypertension exhibit the low-renin type. Increasing age, diabetes mellitus and racial differences are important factors in low-renin primary hypertension. Primary aldosteronism is a common secondary hypertension that manifests as hypertension and reduced PRA. Certain rare monogenic genetic disorders, such as glucocorticoid treatable aldosteronism, Liddle syndrome and episodic salicorticosteronism, also present with low PRA. in addition, certain drugs can lower PRA. 2. Elevated PRA: seen in primary hyperreninemic hypertension, manifested as secondary hypertension secondary to aldosteronism (e.g. unilateral renal artery stenosis, pheochromocytoma, etc.), paraglomerular cell tumor, malignant hypertension, heart failure, hypovolemia, drug therapy (e.g. diuretics, oral contraceptives, etc.).