Renin, also known as angiotensinogenase, is an enzyme that participates in the bodys renin-angiotensin system (RAS) that mediates extracellular volume and arterial vasoconstriction. Thus it regulates the bodys mean arterial blood pressure. Renin is released from the kidneys when there is a drop in blood pressure, a decrease in sodium concentration, or an increase in potassium concentration. It cleaves the blood protein angiotensinogen to form angiotensin I, which is then converted by a second enzyme to angiotensin II. Angiotensin II causes blood vessels to constrict, and it stimulates the production of aldosterone. The overall effect is to raise blood pressure and keep sodium and potassium at normal levels. This test is useful in the diagnosis of renovascular hypertension. INCREASED levels may indicate: addisons disease, cirrhosis, dehydration, hemorrhage (bleeding), high blood pressure, hypokalemia, malignant hypertension, nephrotic syndrome, and renovascular hypertension. REDUCED levels are associated with primary hyperaldosteronism (Conns syndrome) and hyperadrenocorticism (e.g. Cushings syndrome).