Acute kidney failure occurs when the kidneys suddenly lose the ability to filter waste from the blood. When the kidneys lose their filtering capacity, harmful levels of waste can accumulate, and the chemical composition of the blood can become unbalanced. 
 Acute kidney failure, also called acute kidney injury, develops quickly, usually within less than a few days. Acute kidney failure is more common in people who are already hospitalized, especially in those with critical illnesses who need intensive care. 
 Acute kidney failure can be fatal and requires intensive treatment. However, acute kidney failure may be reversible. If, however, you are in good health, you may regain normal or near-normal kidney function. 
 Symptoms 
 Signs and symptoms of acute kidney failure include the following: 
Decrease in the volume of urine excreted (diuresis), although sometimes it remains stable
Fluid retention, causing swelling in the legs, ankles, or feet
Shortness of breath
Fatigue
Disorientation
Sickness
Weakness
Irregular heart rate
Pain or tightness in the chest
Seizures or coma in severe cases
 Sometimes acute kidney failure does not cause signs or symptoms and is found through laboratory tests done for other reasons.