Acute kidney injury (AKI), previously called acute renal failure, is when the kidneys are suddenly unable to filter waste products from the blood. This condition can develop slowly or quickly, and most often occurs in people who are already hospitalized for a different condition.
Treatment depends on the cause and severity of the condition, which can cause mild to complete kidney loss. In many cases, especially if treated early, AKI is reversible, with some people recovering complete kidney function.
There are three main types of acute kidney injury, depending on where the damage occurred:
Prerenal AKI A condition that affects the blood vessels, such as dehydration or cardiovascular disease, prevents enough blood from reaching the kidneys.
Renal AKI The kidneys have direct damage.
Postrenal AKI An obstruction or pressure blocks the tubes that drain urine from the kidneys.
These three causes of acute kidney injury have different treatments and prognoses. Direct damage to the kidneys is often more difficult to fix and recover from, in comparison to obstructions in the blood vessels or urinary system, which can sometimes be resolved quickly. Early identification of the cause of AKI is crucial to guarantee the best treatment and highest likelihood of recovery.
The signs and symptoms of acute kidney injury can vary depending on the individual and severity of the condition. Many people have no symptoms until the condition has progressed to a more severe stage.
When signs and symptoms do occur, they can include the following:
Making less urine than usual
Swelling (edema) in your legs, ankles, or feet due to fluid buildup
Fatigue
Shortness of breath
Nausea
Loss of appetite
Confusion
Flank pain on the side of your back below your rib cage
High blood pressure
Chest pain or pressure
Coma or seizures, when severe
People may also experience signs and symptoms of conditions or infections that cause AKI, such as very low blood pressure or sepsis.
The damage that leads to acute kidney injury has different causes.
Prerenal Acute Kidney Injury
Reduced blood flow to the kidneys can be caused by a variety of health conditions and medication complications:
Use of ACE inhibitors, angiotensin receptor blockers, and nonsteroidal anti-inflammatory drugs (NSAIDs) at high doses, particularly for people with preexisting kidney disease
Kidney damage caused by reduced blood flow is typically reversible.
Renal Acute Kidney Injury
Some health conditions can directly damage the kidneys:
Sepsis is a life-threatening immune response to infection and requires immediate treatment.
Acute tubular necrosis is disorder that damages the tubule cells of the kidneys.
Acute interstitial nephritis is a disorder in which the space between the tubule cells, or the interstitial tissue, become inflamed.
Damage to the renal artery may include thrombosis, embolism, and stenosis.
A wide variety of medications can impair kidney function, and the use of one or more of these drugs often contributes to the development of AKI, especially in people who are already very ill with a different condition. These drugs are known as nephrotoxic medications and include analgesics, antimicrobials, immunosuppressants, and chemotherapy agents.
These drugs tend to cause kidney damage only during specific circumstances, such as when combined with severe dehydration or when used with multiple nephrotoxins. Adjusting or stopping these medications entirely may reverse kidney damage, but this form of kidney disease cannot always be resolved easily, and some of the damage may be irreversible.
Postrenal Acute Kidney Injury
The ureters are the tubes that connect the kidneys to the bladder. Postrenal acute kidney injury occurs when urine cannot freely flow through these tubes, which can cause backflow into the kidneys. A person may not be able to urinate, which can cause the kidneys to swell and experience a number of issues, such as inflammation and scarring.
Obstruction to the ureters can be sudden or gradual, developing over weeks or months. It can be caused by kidney stones, an enlarged prostate, pelvic masses in women, and certain types of cancer. Quickly resolving the obstruction can lead to a rapid recovery, provided that it hasn’t caused much damage to the kidneys themselves.
Risk Factors for Acute Kidney Injury
These risk factors can increase the hazard of developing acute kidney injury:
High LDL (“bad”) cholesterol (hypercholesterolemia)
Low albumin or low sodium levels
Taking nephrotoxic medications
Doctors diagnose acute kidney injury by reviewing an individual’s medical history, doing a physical exam, and performing blood and urine tests. Typically, imaging or biopsies are only done in severe cases or when the cause is unknown.
Medical History Reviewing a person’s medical history can help alert doctors to any medications that may be contributing or if past conditions may be the cause of AKI.
Physical Examination In an exam, a doctor may be able to narrow down a diagnosis. For example, some people develop a skin rash due to an underlying condition, such as acute interstitial nephritis, or medications that can lead to acute kidney injury.
Urine Tests Making less urine is one of the most common symptoms of AKI, so a urine output test can be done to check how much urine is being produced. A doctor may also request a urine sample to test for electrolyte levels and signs of kidney functioning or an infection.
Blood Tests A doctor may do a complete blood count to rule out other conditions. They may also conduct tests to measure the amount of waste products, such as creatinine, estimated glomerular filtration rate, urea nitrogen, sodium, potassium, and bicarbonate. Higher levels of these waste products can indicate that your kidneys are not functioning as they should.
Other Tests A doctor may recommend an ultrasound of the kidneys if they suspect an obstruction. A biopsy of the kidneys is typically only performed when the cause of symptoms is unclear.
Treatment of acute kidney injury depends on the underlying cause. If kidney damage has been caused by an unrelated condition such as a kidney stone, prostate cancer, or heart failure, treating that condition will help the kidneys recover their ability to function.
Immediate treatments can include the following:
Stopping nephrotoxic medications that can cause kidney damage
Providing fluids and monitoring vitals, especially for people with dehydration
Taking antibiotics, if AKI is caused by an infection
Limiting sodium, phosphate, and potassium intake for some people, as these can be difficult for the kidneys to process
Inserting a catheter, if AKI is caused by a blockage
Undergoing dialysis, depending on damage to the kidneys
Restricting water intake for some people
It’s not always possible to prevent acute kidney injury due to certain risk factors, such as age or being hospitalized. However, there are ways to support kidney health and prevent long-term damage:
Get an annual physical. A yearly physical exam will include blood tests that can determine if the kidneys are healthy or not. It can also help a doctor identify any conditions that increase the risk of AKI early.
Stay well hydrated. Dehydration can contribute to AKI, so it’s important to drink plenty of fluids. Aim to drink 1.5 to 2 liters of water every day, unless a doctor has advised otherwise. Drink more water if it’s a very hot day or you’re ill and have a temperature.
Seek help for diarrhea and vomiting. These symptoms can cause dehydration, which can increase your risk of AKI. It’s important to see a doctor as soon as you experience them to prevent developing AKI.
Treat any underlying conditions. Treating an underlying condition like CKD can go a long way in preventing acute kidney injury. Managing CKD can include avoiding the use of NSAIDs, stopping smoking, and avoiding foods high in potassium and salt.
Avoid contrast for imaging when possible. If undergoing certain imaging tests, it’s important to discuss the pros and cons of an iodine contrast dye with a doctor. A doctor may advise against using this dye, as it can affect the kidneys.
It’s important to know if you have any risk factors for acute kidney injury, like CKD or diabetes. If you do, being aware of the symptoms of AKI can help you seek medical attention sooner.
If you’re recovering from acute kidney injury, you can make a few changes to help improve your health and kidney function:
Follow up with your healthcare team regularly, especially about your kidney health.
Eat foods with less potassium, like apples, carrots, green beans, and white rice. The kidneys are responsible for processing potassium, and with loss of function, they can have difficulty removing any excess. Too high levels can cause heart problems.
Limit foods with phosphorus. It can be found in dairy products, oatmeal, dark-colored sodas, and nuts. Your kidneys can have difficulty filtering out excess phosphorus, and too much in your blood can weaken bones.
Limit your salt intake to manage blood pressure by swapping out packaged foods, fast foods, snacks, and processed meats and cheeses. High blood pressure is a risk factor for AKI.
Stay hydrated to avoid dehydration and extra stress on your kidneys.
The outlook for an individual with AKI depends on the underlying cause and severity of kidney damage.
Many people with acute kidney injury can recover completely if the underlying cause is treated early. However, having AKI more than once can worsen kidney function overall.
After acute kidney injury, people may have an increased risk of developing chronic kidney disease, if they don’t already have it. Up to 50 percent of people with AKI develop progressive CKD, while between 3 and 15 percent develop end-stage kidney disease.
Taking care of your overall kidney health and seeking immediate treatment when experiencing any signs or symptoms can aid in your recovery and may help reverse any damage.
Complications of acute kidney injury include the following:
Permanent Kidney Damage In some cases, acute kidney injury may lead to end-stage kidney disease, though this depends on the underlying cause and your kidney function prior to the diagnosis. People with end-stage kidney disease will need dialysis or a kidney transplant.
Fluid Buildup If fluid builds up in the lungs, it can cause shortness of breath and other lung and breathing issues.
High Potassium and Phosphate Levels Too much potassium can lead to arrhythmias, while phosphate can cause bone and joint pain.
Chest Pain This symptom may occur if the lining of the heart (pericardium) becomes inflamed. Other cardiovascular conditions can also arise, such as arrhythmias and cardiac arrest, though these are rare.
Muscle Weakness The kidneys are responsible for regulating electrolyte concentrations in the body. Electrolyte imbalances can cause muscle weakness.
Gastrointestinal Bleeding People may also experience stomach bleeding if the cause of acute kidney injury is related to taking medications like NSAIDs.
In severe cases, such as if the kidneys stop working entirely, acute kidney injury may be fatal.
There are about 13.3 million cases of acute kidney injury every year around the world.
Anyone can get AKI, although it’s more likely in people with certain risk factors, such as being over age 65, having diabetes, and having high blood pressure. This condition is also common in people who are hospitalized, especially those in a critical care setting.
Acute kidney injury creates an immense global burden. It is possible that AKI affects up to 25 percent of people who have been hospitalized and up to 60 percent of those in critical care units. Research suggests that this may be due to developing infections, taking certain medications, and undergoing invasive procedures in hospital settings.
Disparities exist in the mortality rates, outcomes, and treatment of acute kidney injury.
In the United States, mortality rates are consistently higher in rural areas and in older adults, males, and non-Hispanic Black adults.
Research has found that Black and Hispanic children had worse outcomes from 2003 to 2023 compared with white children: They had an increased risk of progression of kidney disease, higher rates of emergency room and ICU visits, and higher use of mechanical ventilation. Asian children also had higher rates of mechanical ventilation.
These disparities may be caused by unequal access to good medical care, as additional research suggests that the connection between race and AKI isn’t as strong for people who have access to health insurance and a higher family income.
CKD is often associated with acute kidney injury. Any condition that puts stress on the kidneys may contribute to this condition, including electrolyte imbalances, kidney disease, and cancer.
Many other conditions may cause or co-occur with acute kidney injury. Some of the most common comorbidities include the following:
You can learn detailed information on keeping your kidneys healthy, kidney conditions and their treatments, and kidney transplants. You can find support through a free information helpline, communities, or peer-mentoring groups. The foundation also offers a way for people to get involved in kidney research.
This charity organization offers support in many forms. It provides information, a space to donate, disaster relief, help with insurance premiums, grants and scholarships, and more. It also has a resource finder to connect you with assistance in your community.
Acute kidney injury results in the kidneys having a decreased ability to filter out waste products. It can be caused by damage to the kidneys or by obstruction in the blood vessels or the urinary system connected to the kidneys.
People may not always experience symptoms with acute kidney injury. But if they do, one symptom is producing less urine than usual.
Acute kidney injury is often reversible, especially when its cause is identified quickly.
