Renin is a proteolytic enzyme released from juxtaglomerular cells of the kidney. The enzyme cleaves a substrate to produce Angiotensin I which in turn produces Angiotensin II. This metabolite plays a key role in various forms of hypertension. Increased levels are seen in Renal hypertension, Addison’s disease and Secondary hypoaldosteronism. Low levels are detected in Hyporeninemic hypoaldosteronism and Primary aldosteronism.