Note: All links within content go to MayoClinic.com

Acute kidney failure is the sudden loss of your kidneys' ability to perform their main function — eliminate excess fluid and waste material from your blood. When your kidneys lose their filtering ability, dangerous levels of fluid and waste accumulate in your body.

Acute kidney failure is most common in people who are already hospitalized, particularly people who need intensive care. Acute kidney failure tends to occur after complicated surgery, after a severe injury or when blood flow to your kidneys is disrupted.

Loss of kidney function may also develop gradually over time, with few signs or symptoms in the early stages. In this case, it's referred to as chronic kidney failure. High blood pressure and diabetes are the most common causes of chronic kidney failure.

Acute kidney failure can be serious and generally requires intensive treatment. Unlike the chronic form, however, acute kidney failure is reversible and if you're otherwise in good health you should recover normal kidney function within a few weeks. If acute kidney failure occurs in the context of severe chronic illness — a heart attack, stroke, overwhelming infection or multiorgan failure — the outcome is often worse.

Signs and symptoms of acute kidney failure may include:

• Decreased urine output, although occasionally urine output remains normal
• Fluid retention, causing swelling in your legs, ankles or feet
• Drowsiness
• Shortness of breath
• Fatigue
• Confusion
• Seizures or coma in severe cases
• Chest pain related to pericarditis, an inflammation of the sac-like membrane that envelops your heart

Some people don't notice any early signs or symptoms, or are more bothered by the underlying problem causing the sudden kidney failure.

Your kidneys are two bean-shaped organs, each about the size of your fist. They're located at the back of your upper abdomen, one on either side of your spine. Your kidneys are part of a system that removes excess fluid and waste material from your blood. Initially, blood enters your kidneys through the renal arteries, which are branches of the aorta — the main artery carrying oxygenated blood from your heart to the rest of your body. From there, blood moves through structures in your kidneys known as nephrons.

Each kidney contains approximately 1 million nephrons, each consisting of a tuft of capillary blood vessels (glomerulus) and tiny tubules that lead into larger collecting tubes. Each tuft of capillaries filters fluid from your bloodstream.

The filtered material, which contains both waste products and substances vital for your health, passes into the tubules. From there, waste byproducts — urea, uric acid and creatinine — are excreted in your urine, while substances your body needs — sugar, amino acids, calcium and salts — are reabsorbed back into your bloodstream.

Causes of acute kidney failure are generally categorized in relation to where and how they affect your kidneys:

• Prerenal. These are problems that interfere with the flow of blood on its way to your kidneys.
• Renal. These are causes that result in direct damage to your kidneys.
• Postrenal. These are problems with the flow of urine after it leaves the kidneys on its way out of your body.

Prerenal
Prerenal problems are among the most common causes of acute kidney failure. Examples of problems that may leave your kidneys with an insufficient blood supply to function properly include:

• Extremely low blood pressure. Severe bleeding, infection in the bloodstream (sepsis), dehydration or shock can all lead to a drastic drop in blood pressure that prevents an adequate amount of blood from reaching your kidneys. These conditions tend to occur after a traumatic injury or as a risk of major surgery.
• Poor heart function. If your heart isn't functioning at full capacity, such as during a heart attack or with congestive heart failure, the result can be reduced blood flow to your kidneys.
• Low blood volume. Severe dehydration — which can be brought on by prolonged vomiting or diarrhea, heatstroke or major burns — results in excessive loss of fluid, diminishing the volume of blood in your body and the amount available to your kidneys.

Renal
Conditions that may affect the structure and function of the kidney itself, potentially leading to acute kidney failure, include:

• Disorders that reduce blood supply in your kidneys. Any number of disorders can lead to decreased blood supply in your kidneys, which can lead to organ damage and acute kidney failure. One example is atheroembolic kidney disease.

  Atheroembolic kidney disease can occur when masses of cholesterol and cellular debris (plaques) accumulate in arteries and harden in a process called atherosclerosis. If a plaque is injured or disturbed — cardiac catheterization, a procedure used to conduct diagnostic tests and treatments on the heart, is a common cause — pieces of it may break off into your bloodstream and move throughout your body. These moving pieces are called emboli. When these emboli move to your kidneys, the cholesterol emboli accumulate in small blood vessels (arterioles). Within the arterioles, these emboli can produce severe inflammation, leading to decreased blood supply and acute kidney failure.

  Other causes of reduced blood supply include a blood disorder called idiopathic thrombocytopenic purpura, development of blood clots in kidney vessels, a reaction to a blood transfusion, or a sudden onset of severe high blood pressure (malignant hypertension).

• Hemolytic uremic syndrome. This condition, which is associated with certain strains of Escherichia coli (E. coli) bacteria, is a leading cause of acute kidney failure in infants and young children. The bacterium causes inflammation of the intestine. It also produces a toxin that causes damage and swelling in the lining of blood vessels, especially the small blood vessels (glomerular capillaries) in the kidneys. As red blood cells travel through the damaged blood vessels, they're often broken apart (hemolysis). This complex condition may result in acute kidney failure.

• Inflammation in the kidneys. Acute kidney failure may result from sudden inflammation of the spaces between the glomeruli and the tubules (acute interstitial nephritis) and inflammation of the glomeruli (acute glomerulonephritis). Acute interstitial nephritis is usually associated with an allergic reaction to a drug. Examples include certain antibiotics — especially streptomycin or gentamicin — and common pain medications, such as aspirin and ibuprofen (Advil, Motrin, others). Antibiotics pose a greater risk of acute kidney failure for people who already have liver or kidney disease or who use diuretics or other drugs that affect your kidneys.

  Acute glomerulonephritis may be associated with immune diseases, such as lupus or IgA nephropathy (Berger's disease). It may also follow an infection in another part of your body, such as strep throat, infection of a heart valve (endocarditis), typhoid fever, syphilis and malaria. Viruses that cause AIDS, mononucleosis, mumps, measles or hepatitis also may trigger glomerulonephritis.

• Toxic injury. Because the main purpose of your kidneys is to filter toxins from your body, your kidneys are particularly vulnerable to toxic injury. Exposure to toxic substances — such as excessive amounts of alcohol, cocaine, heavy metals, solvents and fuels — can induce acute kidney failure. Certain drugs also have the potential to injure the tubules in your kidneys, including chemotherapy drugs and contrast dyes used in medical tests, such as arteriography. Contrast dyes are a common cause of acute renal failure, especially in people with diabetic kidney disease or multiple myeloma, a type of cancer.

Postrenal
Postrenal causes of acute kidney failure are generally related to obstruction of the flow of urine out of your kidneys on the way out of your body. This may occur at the level of the tubes that lead from your kidneys to your bladder (ureters), or at the bladder level (urethral obstruction).

• Ureter obstruction. Kidney stones in both ureters (or in a single ureter if only one kidney is functioning) or tumors pushing in on the ureters can cause obstruction at this level.
• Bladder obstruction. In the bladder, the most common cause of obstruction in men is an enlarged prostate, which causes obstruction at the bladder outlet. Other obstructive bladder causes, in both men and women, include a bladder stone, blood clot, tumor or a nerve disorder that prevents the bladder from contracting properly.

Acute kidney failure almost always occurs in connection with another medical condition or event. In fact, most people who experience acute kidney failure are already in the hospital for other reasons.

Severe injuries or burns to your body and complicated surgery increase your risk of acute kidney failure, as can an overwhelming infection. In addition, exposure to toxic substances, drug overdose, excessive use of alcohol, and long-term use of pain medications, such as aspirin, acetaminophen (Tylenol, others) and ibuprofen (Advil, Motrin, others), can increase your vulnerability to kidney failure. Sometimes, a person with a life-threatening infection who receives an antibiotic, such as streptomycin or gentamicin, may go into acute kidney failure.

X-ray tests that use contrast dyes to outline blood vessels may increase the risk of acute kidney failure particularly in people who have diabetes-related kidney disease or multiple myeloma, a type of cancer that affects your plasma cells, a special type of white blood cell.

Medical conditions that increase your risk of acute kidney failure include:

• Chronic infection
• Diabetes
• High blood pressure
• Heart failure
• Various blood disorders
• Immune disorders, such as lupus, IgA nephropathy and scleroderma
• Kidney diseases
• Liver diseases
• Prostate gland enlargement
• Bladder outlet obstruction

Call your doctor promptly if you experience decreased urination or no urine output at all, fluid retention or other signs and symptoms of acute kidney failure. If you or someone you know has undergone severe injuries, burns or heatstroke, or is having seizures or slips into a coma, call 911 or your local emergency medical assistance number.

If your doctor suspects acute kidney failure, he or she is likely to order urine and blood tests to check for chemical abnormalities such as increased levels of urea, creatinine and potassium. Your doctor may measure both the quantity and quality of your urine output.

Early changes associated with acute kidney failure:

• Daily urine output usually falls to less than 500 milliliters (2 cupfuls).
• Blood urea and creatinine levels rise rapidly.
• Blood potassium level increases rapidly, often to life-threatening levels.
• Retention of sodium and water leads to swelling (edema) and lung congestion plus changes in electrolyte levels in your blood. Electrolytes are minerals such as sodium, potassium and calcium that maintain the balance of fluids in your body.

To rule out an obstruction as the cause of your kidney failure, your doctor may perform an abdominal ultrasound exam. This test uses high-frequency sound waves and computer technology to generate images of your kidneys. Ultrasound scans are noninvasive and usually take less than 30 minutes. Ultrasound is the imaging test most commonly used in diagnosing kidney failure, but your doctor may also order an abdominal computerized tomography (CT) or magnetic resonance imaging (MRI) scan.

In a few cases, your doctor may remove a small sample (biopsy) of kidney tissue and send it to a laboratory for microscopic examination to identify the cause of acute kidney failure.

The sooner the cause of your acute kidney failure is resolved, the more likely your kidney function will recover. Prior good health also increases your chances of a successful recovery.

Occasionally, acute kidney failure may lead to chronic kidney failure when the kidneys fail to heal completely. If organ damage is severe, kidney function may be permanently lost, resulting in end-stage renal disease. People with end-stage renal disease require either permanent dialysis — a mechanical filtration system for removing toxins and waste from your body — or a kidney transplant to survive.

Mortality rates are highest for people whose acute kidney failure follows an operation or a traumatic accident, or among people with severe chronic medical problems. Kidney failure can interfere with your ability to fight harmful bacteria and viruses and can impair your blood-clotting ability, predisposing you to infection and excessive bleeding.

Other factors that can adversely affect the outcome of acute kidney failure include multiorgan failure, multiple blood transfusions, a recent history of stroke or heart attack, or a postoperative stroke, advanced age, infection, gastrointestinal bleeding and pre-existing malnutrition.

The first goal is to treat the illness or injury that originally damaged your kidneys. Once that's under control, the focus will be on preventing the accumulation of excess fluids and wastes in your blood while your kidneys heal. This is best accomplished by limiting your fluid intake and following a high-carbohydrate, low-protein, low-potassium diet.

Your doctor may prescribe calcium, glucose or sodium polystyrene sulfonate (Kayexalate) to prevent the accumulation of high levels of potassium in your blood. Too much potassium in the blood can cause dangerous irregular heartbeats (arrhythmias).

Dialysis
Most of the time, you also need to undergo temporary dialysis to help remove toxins and excess fluids from your body. Dialysis is a mechanical way of filtering waste from your blood. It can replace the function of your kidney, albeit imperfectly, while your kidneys are healing. Dialysis treatment for acute kidney failure is usually done at a hospital or dialysis center, not at home.

The most common form of dialysis used for acute kidney failure is known as hemodialysis. It removes extra fluids, chemicals and wastes from your bloodstream by filtering your blood through an artificial kidney (dialyzer). Blood is pumped out of your body to the artificial kidney through a vascular access that's created surgically, usually in your arm or leg. Your blood moves across membranes inside the artificial kidney that filter out waste. Less than 1 cup of blood is outside your body in the dialyzer and tubing at any one time.

It's often not possible to prevent kidney failure. But you may reduce your risk by following these suggestions:

• Don't abuse alcohol or drugs, including over-the-counter pain medications such as aspirin, acetaminophen and ibuprofen. Avoid long-term exposure to heavy metals, such as lead, as well as to solvents, fuels and other toxic substances.
• Carefully follow all of your doctor's recommendations for managing your condition if you have a chronic medical condition that increases your risk of kidney failure.

If you're at high risk of kidney damage induced by contrast dye used for certain X-rays — for example, if you have diabetes or multiple myeloma — your doctor may prescribe you a dose of acetylcysteine (Mucomyst) before the procedure. This medicine can help prevent acute kidney failure under these circumstances.