Acute Kidney Failure Causes
Causes of acute kidney failure fall into one of the following categories:
Prerenal: Problems affecting the flow of blood before it reaches the kidneys
Postrenal: Problems affecting the movement of urine out of the kidneys
Renal: Problems with the kidney itself that prevent proper filtration of blood or production of urine
Prerenal failure
Prerenal failure is the most common type of acute renal failure (60%-70% of all cases). The kidneys do not receive enough blood to filter. Prerenal failure can be caused by the following conditions:
Dehydration: – From vomiting, diarrhea, water pills, or blood loss
Disruption of blood flow to the kidneys from a variety of causes:
Drastic drop in blood pressure from major surgery with blood loss, severe injury or burns, or infection in the bloodstream (sepsis) causing blood vessels to inappropriately relax
Blockage or narrowing of a blood vessel carrying blood to the kidneys
Heart failure or heart attacks causing low blood flow
Liver failure causing changes in hormones that affect blood flow and pressure to the kidney
There is no actual damage to the kidneys early in the process with prerenal failure. With appropriate treatment, the dysfunction usually can be reversed. Prolonged decrease in the blood flow to the kidneys, for whatever reason, can however cause permanent damage to the kidney tissues.
Postrenal failure
Postrenal failure is sometimes referred to as obstructive renal failure, since it is often caused by something blocking elimination of urine produced by the kidneys. It is the rarest cause of acute kidney failure (5%-10% of all cases). This problem can be reversed, unless the obstruction is present long enough to cause damage to kidney tissue.
Obstruction of one or both ureters can be caused by the following:
Kidney stone: usually only on one side
Cancer of the urinary tract organs or structures near the urinary tract that may obstruct the outflow of urine
Medications
Obstruction at the bladder level can be caused by the following:
Bladder stone
Enlarged prostate (the most common cause in men)
Blood clot
Bladder cancer
Neurologic disorders of the bladder impairing its ability to contract
Treatment consists of relieving the obstruction. Once the blockage is removed, the kidneys usually recover in one to two weeks if there is no infection or other problem.
Renal damage
Primary renal damage is the most complicated cause of renal failure (accounts for 25%-40% of cases). Renal causes of acute kidney failure include those affecting the filtering function of the kidney, those affecting the blood supply within the kidney, and those affecting the kidney tissue that handles salt and water processing.
Some kidney problems that can cause kidney failure include:
Blood vessel diseases
Blood clot in a vessel in the kidneys
Injury to kidney tissue and cells
Glomerulonephritis
Acute interstitial nephritis
Acute tubular necrosis
Glomerulonephritis: The glomeruli, the initial filtration system in the kidney, can be damaged by a variety of diseases, including infections. The resulting inflammation impairs kidney function.
A common example is strep throat. Streptococcal bacterial infections may damage the glomeruli.
Glomerular disorder symptoms may include dark-colored urine (like cola or tea) and back pain.
Other symptoms include producing less urine than usual, blood in the urine, high blood pressure, and body swelling (retaining water).
Treatment usually consists of medications and, if kidney function fails significantly, dialysis may be needed to remove life-threatening waste products that cannot be excreted.
Acute interstitial nephritis: This is a sudden decline in kidney function caused by inflammation of interstitial kidney tissue which primarily handles salt and water balance rather than the filtering of wastes.
Medications such as antibiotics, anti-inflammatory medicines (for example, aspirin, ibuprofen), and water pills (diuretics) are the most common causes.
Other causes include infections and immune-related diseases such as lupus, leukemia, lymphoma, and sarcoidosis.
It is usually reversible if the kidney damage is not severe.
Treatment consists of withdrawal of offending drugs, treatment of infection, and dialysis in cases of very low kidney function.
Acute tubular necrosis: The kidney tubules are damaged and do not function normally. Tubular necrosis is usually the end result from the other causes of acute renal failure. The tubules are delicate structures that handle much of the kidney’s filtration function. When there is necrosis, the cells that form the tubules become dysfunctional and “die”.
This condition accounts for 90% of cases of primary acute kidney failure.
Causes include shock (decreased blood supply to the kidneys), drugs (especially antibiotics) and chemotherapy agents, toxins and poisons, and dyes used in certain kinds of x-rays.
Some people produce much less urine than usual. Other symptoms of acute tubular necrosis include tiredness, swelling, lethargy, nausea, vomiting, abdominal pain, loss of appetite, and rash. Sometimes there are no symptoms.
Treatment depends on the cause of the damage and may consist of discontinuing problem medications, replenishing body fluids, and improving blood flow to the kidney. A diuretic may be given to increase urine production if the total body water level is too high. Medications may be given to correct blood chemistry imbalances.
If there is no recovery of the patient’s kidneys and these treatments do not sufficiently substitute for the lost kidney function, the patient will need regular dialysis or may be a candidate for kidney transplantation.
Acute Kidney Failure Symptoms
The following symptoms may occur with acute kidney failure. Some people have no symptoms, at least in the early stages. The symptoms may be very subtle.
Decreased urine production
Body swelling
Problems concentrating
Confusion
Fatigue
Lethargy
Nausea, vomiting
Diarrhea
Abdominal pain
Metallic taste in the mouth
Seizures and coma may occur in very severe acute kidney failure.
Exams and Tests
Many people with acute renal failure notice no symptoms. Even with symptoms, they are nonspecific, meaning they could be caused by many different conditions. A physical examination typically reveals few, if any, abnormal findings.
Kidney failure is often detected from blood or urine tests. These tests might be ordered because the patient is in the hospital for another reason, because they don’t feel well and can’t tell why, or as part of a routine health screening.
Levels of urea (blood urea nitrogen [BUN]) and creatinine are high in kidney failure of prerenal origin. This is called azotemia.
Electrolyte levels in the blood may be abnormally high or low because of improper filtering.
When the duration and severity of kidney failure is severe, the red blood cell count may be low. This is called anemia.
The amount of urine produced over a period of hours may also be measured for quantity and quality or the amount of wastes being excreted. When kidney tissue is injured, protein and desirable substances may be inappropriately excreted in the urine. In some cases, the amount of urine remaining in the bladder after urination will be measured by inserting a catheter (a thin, rubber tube) that drains the bladder.
Urine retained in the bladder after urinating suggests postrenal failure, usually due to prostate enlargement in men.
The urine may be dark, indicating that creatinine and other substances are concentrated.
The urine will be examined under a microscope to detect signs of specific kidney problems. Some of these signs include blood, pus, and solid materials called casts.
Electrolyte levels in the urine may help pinpoint the exact cause of the kidney failure.
If the diagnosis is not certain after laboratory tests, an ultrasound of the kidneys and bladder may be done. These can help reveal signs of specific causes of kidney failure.
In some cases, tissue samples of the kidneys are taken (biopsy) to find the cause of the renal failure.