The kidneys are a pair of organs located in the back of the abdominal cavity at the level of the costal arch. Their function is to regulate the water and salt balance of the body as well as blood pressure. They fulfil an important detoxification function by excreting water-soluble metabolic products through the urine. The human body normally produces about 1.5-2 litres of urine per day. The colour is normally clear to yellowish, although this changes depending on how much fluid intake the individual has had. The kidneys are also involved in blood formation trough hormonal feedback mechanisms, among other functions.

A wide variety of changes and diseases can affect the kidneys. The spectrum ranges from findings with very little severity to acutely threatening diseases with the need for immediate intervention.