Renin Activity is also known as Plasma renin activity (PRA) or the renin (active) assay or random plasma renin. It is a measurement of the movement of the plasma enzyme renin, which plays the main role in the body's parameter of blood pressure, thirst, and urine output. PRA is sometimes measured, specifically in case of certain diseases which present with hypertension or hypotension. PRA is also elevated in certain tumors. A PRA measurement may be linked to a plasma aldosterone concentration as an aldosterone-to-renin ratio.