Kidney provides two main functions, cleaning the blood and removing salt and water from the body. There are two main kinds of kidney disease - Acute Kidney Injury and Chronic Kidney Disease. Acute Kidney Injury (AKI) is when the kidney has been normal but a sudden event causes reduction or decrease of the function of the kidney within a few days or weeks. In these conditions, if the cause is identified and treated the kidney function may improve and may even return to normal.