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Acute Kidney Injury

(Acute Kidney Failure; Acute Renal Failure)


Anna Malkina

, MD, University of California, San Francisco

Reviewed/Revised Oct 2023
Topic Resources

Acute kidney injury is a rapid (days to weeks) decline in the kidneys’ ability to filter metabolic waste products from the blood.

  • Causes include conditions that decrease blood flow to the kidneys, that damage the kidneys themselves, or that block drainage of urine from the kidneys.

  • Symptoms may include swelling, nausea, fatigue, itching, difficulty breathing, and symptoms of the disorder that caused the acute kidney injury.

  • Serious complications include heart failure and high levels of potassium in the blood.

  • Diagnosis is with blood and urine tests and usually imaging studies.

  • Treatment involves correcting the cause of acute kidney injury and sometimes doing dialysis.

The Kidneys

Acute kidney injury can result from any condition that decreases the blood supply to the kidneys, any disease or toxic substances (also called toxins) affecting the kidneys themselves, or any condition that obstructs urine flow anywhere along the urinary tract.

Overview of Intrarenal Acute Kidney Injury

In many people, no cause of acute kidney injury can be identified.

If both kidneys function normally, damage to one kidney (for example, due to blockage by a kidney stone Stones in the Urinary Tract Stones (calculi) are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine. Tiny stones may cause no symptoms, but larger stones... read more Stones in the Urinary Tract ) does not usually cause major problems because the remaining good kidney can compensate and usually maintain near-normal kidney function, as determined by laboratory measurements. Thus, acute kidney injury may be hard for doctors to detect. For acute kidney injury to cause significant problems, usually both kidneys must be damaged or function abnormally.


Symptoms of Acute Kidney Injury

Symptoms depend on the

  • Severity of decline in kidney function

  • Rate of decline in kidney function

  • Cause of decline in kidney function

Early symptoms include

  • Water retention, causing weight gain and swelling of the feet and ankles or puffiness of the face and hands

  • Decreased amount of urine

The amount of urine (which for most healthy adults is between 3 cups [about 750 milliliters] and 2 quarts [about 2 liters] per day) often decreases to less than 2 cups (about 500 milliliters) per day or stops completely. Very little urine production is called oliguria, and no urine production is called anuria. However, some people with acute kidney injury continue to produce normal amounts of urine.

Later, as acute kidney injury persists and waste products accumulate in the body, people may experience

  • Fatigue

  • Decreased ability to concentrate on mental tasks

  • Loss of appetite

  • Nausea

  • Overall itchiness (pruritus)

The passing of cola-colored urine may indicate a number of kidney diseases that damage the glomeruli, the filtering units of the kidney. The brown color results from blood passing through the filtering units and may be the first sign of a condition known as a glomerulonephritis Glomerulonephritis Glomerulonephritis is a disorder of glomeruli (clusters of microscopic blood vessels in the kidneys with small pores through which blood is filtered). It is characterized by body tissue swelling... read more (inflammation of the filtering units). Examples include postinfectious glomerulonephritis, antiglomerular basement membrane disease, and lupus nephritis.

If acute kidney injury is caused by a blockage (an obstruction), the backup of urine within the kidneys causes the drainage system to stretch (a condition called hydronephrosis—see figure ). Urinary tract obstruction Urinary Tract Obstruction Urinary tract obstruction is a blockage that inhibits the flow of urine through its normal path (the urinary tract), including the kidneys, ureters, bladder, and urethra. Blockage can be complete... read more often causes a constant dull ache under the lower ribs but may cause crampy pain—ranging from mild to excruciating—usually along the sides (flanks) of the body. Some people with hydronephrosis have blood in their urine from an underlying cause, such as kidney stones. If the obstruction is located below the bladder, the bladder will enlarge. If the bladder enlarges rapidly, people are likely to feel severe pain and pressure in the pelvis, just above the pubic bone. If the bladder enlarges slowly, pain may be minimal, but the lower part of the abdomen may swell because of the enlarged bladder.

If acute kidney injury develops during hospitalization, the condition often relates to some recent injury, surgery, medication, or illness such as infection. Symptoms due to the cause of the acute kidney injury may predominate. For example, high fever, life-threateningly low blood pressure (shock Low Blood Pressure and Shock ), and symptoms of heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more Heart Failure (HF) or liver failure Liver Failure Liver failure is severe deterioration in liver function. Liver failure is caused by a disorder or substance that damages the liver. Most people have jaundice (yellow skin and eyes), feel tired... read more may occur before symptoms of kidney failure and be more obvious and urgent.

Diagnosis of Acute Kidney Injury

  • Blood and urine tests

  • Imaging tests

Did You Know...

  • A disorder must affect both kidneys to cause kidney failure.

The doctor evaluates whether the person has acute kidney injury and, very importantly, its cause.

Physical examination

The physical examination findings may help doctors identify the cause of the acute kidney injury. For example, an enlarged bladder may indicate obstruction of the urinary tract causing hydronephrosis.

Blood tests

Blood tests that measure levels of creatinine and urea nitrogen in the blood are needed to confirm the diagnosis. A progressive daily rise in creatinine indicates acute kidney injury.

The level of creatinine is also the best indicator of the degree or severity of kidney function decline. The higher the level, the more severe the decline in kidney function is likely to be.

Other blood tests detect metabolic imbalances that occur if the decline in kidney function is severe, such as an increase in blood acidity (acidosis Acidosis Acidosis is caused by an overproduction of acid that builds up in the blood or an excessive loss of bicarbonate from the blood (metabolic acidosis) or by a buildup of carbon dioxide in the blood... read more , which means low bicarbonate level), a high potassium level (hyperkalemia Hyperkalemia (High Level of Potassium in the Blood) In hyperkalemia, the level of potassium in blood is too high. A high potassium level has many causes, including kidney disorders, medications that affect kidney function, and consumption of... read more ), a low sodium level (hyponatremia Hyponatremia (Low Level of Sodium in the Blood) In hyponatremia, the level of sodium in blood is too low. A low sodium level has many causes, including consumption of too many fluids, kidney failure, heart failure, cirrhosis, and use of diuretics... read more ), low calcium (hypocalcemia Hypocalcemia (Low Level of Calcium in the Blood) In hypocalcemia, the calcium level in blood is too low. A low calcium level may result from a problem with the parathyroid glands, as well as from diet, kidney disorders, or certain medications... read more ), and a high phosphorus level (hyperphosphatemia Hyperphosphatemia (High Level of Phosphate in the Blood) In hyperphosphatemia, the level of phosphate in blood is too high. (See also Overview of Electrolytes and Overview of Phosphate's Role in the Body.) Phosphate is one of the body's electrolytes... read more ).

Urine tests

Urine tests, such as urinalysis and measurement of certain electrolytes (sodium, potassium, calcium, phosphate), may enable doctors to determine whether the cause of kidney injury is insufficient blood flow to the kidneys, damage to the kidneys, or urinary obstruction.


X-rays of the arteries or veins that lead to and from the kidneys (angiography Angiography Angiography is a type of medical imaging that uses x-rays and a contrast agent to produce images of blood vessels. In angiography, x-rays are used to produce detailed images of blood vessels... read more ) may be done if obstruction of blood vessels is the suspected cause. However, angiography is done only when other tests do not provide enough information, because angiography uses an intravenous contrast agent that contains iodine, which carries a risk of additional kidney damage.

Magnetic resonance angiography (MRA) can provide information similar to that provided by angiography. However, MRA has traditionally used gadolinium, a substance that, in people who have severely reduced kidney function, rarely causes a disorder that triggers production of scar tissue in the body (nephrogenic fibrosing dermopathy). The risk of this condition decreased with the newer gadolinium formulations, so MRA could be a good option after discussion with the health care team. If other tests do not reveal the cause of kidney injury, a biopsy Kidney biopsy Site-specific biopsies and cell sampling are also used in the evaluation of people with suspected kidney and urinary tract disorders. (See also Overview of the Urinary Tract.) A kidney biopsy... read more may be necessary to determine the diagnosis and the prognosis.

Treatment of Acute Kidney Injury

  • Treating any treatable causes

  • Restricting or adjusting fluid intake, electrolytes, and doses of medications eliminated through the kidneys

  • Sometimes starting dialysis

Some complications of acute kidney injury are serious and may even be life-threatening. People may need to be treated in a critical care unit (also called an intensive care unit [ICU]).

Any treatable cause of acute kidney injury is treated as soon as possible. For example, if obstruction is the cause, a catheter (a tube placed into the bladder to remove urine), cystoscopy (procedure to look inside the bladder with a camera to eliminate the blockage), or surgery may be needed to relieve the obstruction.

Often, the kidneys can heal themselves, especially if the kidney injury has existed for only a few days and there are no complicating problems such as infection. During this time, measures are taken to prevent the decreased kidney function from causing serious problems. Such measures may include the following:

  • Restricting use of certain medications that may be harsh on the kidneys

  • Restricting fluids, sodium, phosphorus, and potassium in the diet

  • Maintaining good nutrition

  • Giving medications if blood levels of potassium or phosphate are too high

  • Starting dialysis

Dietary measures

Salt (sodium) and potassium intake is usually restricted. Fluid intake is restricted to replacing the amount lost from the body, unless fluid is needed because there is too little blood flowing to the kidneys. Weight is measured every day because a change in weight is a good indicator of whether there is too much or too little fluid in the body.

A healthy diet is provided to people whose condition allows them to eat. Moderate amounts of protein are acceptable, typically 0.8 to 1 gram per kilogram of body weight (0.4 to 0.5 gram per pound) per day. Restricting the intake of foods that are high in phosphorus, such as dairy products, liver, legumes, nuts, and most soft drinks, lowers the phosphate concentration in the blood.


Potassium-lowering medications are sometimes given by mouth or rectally to treat a high level of potassium in the blood. Phosphorus-lowering medications (also called phosphorus binders) may be given by mouth with meals to prevent or treat a high level of phosphorus in the blood.


Kidney Failure: Dialysis

Acute kidney injury may be prolonged, necessitating removal of waste products and excess water. Waste removal can be done through dialysis, usually hemodialysis Hemodialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more Hemodialysis . If loss of kidney function is predicted to be prolonged or changes in diet and medication(s) are predicted to be ineffective, dialysis is started. Dialysis helps control the complications of acute kidney injury. Dialysis may be needed only temporarily, until the kidneys recover their function, usually in several days to several weeks, sometimes after hospital discharge. If the kidneys do not recover, dialysis (hemodialysis Hemodialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more Hemodialysis or peritoneal dialysis Peritoneal dialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more Peritoneal dialysis ) is continued indefinitely or kidney transplantation Kidney Transplantation Kidney transplantation is the removal of a healthy kidney from a living or recently deceased person and then its transfer into a person with end-stage kidney failure. (See also Overview of Transplantation... read more Kidney Transplantation is pursued.

Treament of acute kidney injury caused by obstruction

Fluids are not restricted in people who are recovering from acute kidney injury caused by obstruction. During the recovery period, the kidneys are unable to reabsorb sodium and water normally, and a large amount of urine may be produced for a period of time after the obstruction is relieved. During recovery, people may need replacement of fluids and also electrolytes, such as sodium, potassium, and magnesium.

Prognosis for Acute Kidney Injury

Acute kidney injury and its immediate complications, such as water retention, high acid and potassium levels in the blood, and increased urea nitrogen in the blood, can often be treated successfully. Typically, prognosis is favorable for people whose acute kidney injury is due to decreased blood flow because body fluids have been lost through bleeding, vomiting, or diarrhea—conditions that are reversible with treatment. Prognosis is worse for people in whom some other organs (such as the heart, lungs, or liver) are failing at the same time. How long the person requires dialysis therapy Dialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more Dialysis (for example, from days to life-long) depends on the person's overall health and kidney health before acute kidney injury develops.

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