The kidneys are responsible for filtering blood and removing waste from the body through the urine. Acute renal failure occurs when one or both kidneys suddenly stop functioning, leading to a buildup of fluid, toxins and abnormal levels of minerals in the body. Reduced blood supply and/or damage to the essential filtering structures of the kidneys can lead to acute renal failure. Depending upon the underlying cause and characteristic symptoms, the condition is classified into one of three types.
Prerenal Acute Renal Failure
According to the American Academy of Family Physicians, approximately 60 to 70 percent of acute renal failure cases are classified as prerenal, characterized by significantly reduced blood flow to the kidneys. Poor circulation of blood through the kidneys reduces their ability to function effectively. As a result, sodium and water may re-circulate through the body rather than exiting through the urine, causing decreased urine output and swelling of the extremities, according to Merck.com. Prerenal acute renal failure is often caused by chronic medical conditions that interfere with blood circulation throughout the body, especially atherosclerosis, cardiovascular disease and other heart conditions. Dehydration is another common cause of prerenal acute renal failure, according to NephrologyChannel.com. Though the condition is sometimes reversible by treating the underlying medical condition, it can lead to life-threatening illness and multi-organ failure if not treated promptly.
Intrinsic Acute Renal Failure
Intrinsic acute renal failure represents approximately 40 percent of all acute renal failure cases and is characterized by damage to the functional components of both kidneys, according to NephrologyChannel.com. The vast majority of these cases are caused by inadequate blood and oxygen supply to the kidneys and/or toxins, each of which can lead to damage to the kidney’s tubules--structures in the kidney that collect filtered plasma and turn it into urine. Those with intrinsic acute renal failure may develop hypertension, protein in the urine, edema, rash, fever, joint pain, headaches and dizziness. Due to severely impaired functioning in both kidneys, affected patients may also develop electrolyte imbalances, including elevated levels of potassium, magnesium and phosphates, and abnormally low levels of calcium in the bloodstream.
Postrenal Acute Renal Failure
Postrenal acute renal failure is the least common type of acute renal failure, representing approximately 5 to 10 percent of all cases, according to the American Academy of Family Physicians. The condition occurs as a result of an acute blockage in the urinary tract, bladder, ureter(s)--tubes that deliver urine from the kidneys to the bladder--or tubules at the end of nephrons--the filtering components of the kidneys. Particularly common among older men with prostate problems, this condition can lead to symptoms such as lower back pain, high blood pressure, problems urinating, edema and blood in the urine.
