Prerenal and Intrinsic Renal Failure
Acute renal failure has been divided into three diagnostic categories: prerenal, intrarenal (also called organic and intrinsic), and postrenal failure. Prerenal failures are responses of a structurally intact kidney to extrarenal processes. In most instances, the kidneys recover rapidly as soon as the course is reversed. Intrinsic renal failure is caused by structural changes within the kidneys, and postrenal failure is due to structural abnormalities in the ureters, bladder, or urethra. Prerenal failure usually is due to decreased effective blood volume or heart failure from such conditions as dehydration or shock. Laboratory studies demonstrate hemoconcentrates, few abnormalities of the urine, preserved tubular integrity, high urine-specific gravity, and low urinary sodium.