During the last few years, uniform criteria have been created for the diagnosis of acute renal insufficiency and its degree of severity. The term acute kidney injury covers all forms of acute damage regardless of the pathogenic mechanism. Acute kidney injury has been conventionally diagnosed on the basis of increased creatinine level or decreased urine volume resulting from impaired glomerular filtration. The detection of tubular injury enables an earlier diagnosis of acute kidney injury, because impairment of glomerular filtration often precedes the tubular injury. New markers are becoming available, which are more sensitive and more specific for kidney injury.