Acute renal failure. 1. Classification, evaluation, and clinical consequences.

Urinalysis and urine chemistries are most helpful in determining whether acute renal failure is due to a prerenal, renal, or postrenal cause. A plain film of the abdomen should be obtained, with ultrasound or computed tomography also being done if obstruction is suspected. When prerenal and postrenal causes have been excluded, the cause should be considered to be acute tubular necrosis, which progresses through initiating, oliguric (or sometimes nonoliguric), diuretic, and recovery phases. Acute tubular necrosis can produce a variety of clinical consequences affecting the entire body, including hyperkalemia, acidosis, hypocalcemia, anemia, and infection, as well as various cardiovascular, neurologic, and gastrointestinal problems.