Acute kidney injury is common; it is seen in 13–18% of all people admitted to hospital. It increases both morbidity and mortality, although how often acute kidney injury is the cause is difficult to assess because it can often be a symptom of an underlying condition.

Acute kidney injury is generally subdivided into 4 types:

  • pre-renal – in which the kidneys are structurally intact but the body is responding to severe fluid loss or hypotension

  • intrinsic – in which ischaemic, inflammatory, cytotoxic or physical injury has damaged the kidney

  • post-renal – in which mechanical urological obstruction prevents urine being passed

  • acute-on-chronic – in which chronic kidney disease is already present.

Acute kidney injury is usually temporary and treatable. However, sometimes it is not completely reversible and can increase the risk of future acute kidney injury. Severe acute kidney injury can lead to, or may already be associated with, multi-organ failure; emergency treatment, dialysis and extended care may be needed, and mortality rates can be high.