Acute Kidney Injury (AKI): Causes, Symptoms, Diagnosis, Treatment and Prevention

Acute kidney injury (AKI) is a sudden decline in kidney function that can develop over a short period of time. It was formerly commonly called acute renal failure. AKI can occur because the kidneys do not receive enough blood flow, because kidney tissue is directly damaged, or because urine flow becomes blocked.

Although some people recover completely, AKI can become serious when waste products, excess fluid, potassium, or acids build up in the body. Early recognition and treatment of the underlying cause are important.

This guide explains what AKI is, common causes, warning signs, how doctors evaluate it, treatment approaches, possible complications, and ways to reduce risk.

Medical disclaimer: This article is for general educational purposes only and is not a substitute for diagnosis or treatment from a qualified healthcare professional. If you have very little or no urine, severe breathing difficulty, confusion, significant swelling, chest symptoms, or another serious or rapidly worsening symptom, seek urgent medical care.

What Is Acute Kidney Injury?

Your kidneys continuously filter the blood and help remove waste products and excess fluid through urine. They also help maintain the body's balance of electrolytes and other substances.

With acute kidney injury, kidney function decreases suddenly. Blood tests may show a rise in serum creatinine, while urine production may decrease in some people.

AKI does not always cause obvious symptoms at first. In some cases, it is discovered through blood or urine testing performed during treatment for another illness.

The condition can range from mild to life-threatening, depending on its cause, severity, and the person's overall health.

What Causes AKI?

Doctors commonly consider three broad categories when looking for the cause of AKI.

1. Reduced Blood Flow to the Kidneys

This is sometimes described as a prerenal cause. The kidneys may receive inadequate blood flow because of conditions such as:

Severe dehydration or fluid loss
Very low blood pressure
Major bleeding
Severe infection or sepsis
Certain heart or circulatory problems
Serious illness or surgery

If reduced blood flow is recognized and corrected promptly, kidney function may improve. However, prolonged inadequate blood flow can contribute to direct kidney damage.

2. Direct Kidney Damage

AKI can also occur when the kidney's filtering structures or tubules are injured.

Possible causes include:

Acute tubular injury or necrosis
Certain autoimmune kidney diseases
Severe infections
Some medications or other substances that can injure the kidneys
Reduced oxygen delivery to kidney tissue
Certain vascular problems

Acute tubular injury is an important cause of AKI, particularly in seriously ill hospitalized patients.

3. Blocked Urine Flow

A blockage after urine has been produced can also cause kidney dysfunction. Examples include:

Kidney or urinary tract stones
An enlarged prostate
Certain tumors or masses
Other forms of urinary tract obstruction

Doctors may use imaging, such as ultrasound, when obstruction is suspected.

Symptoms of Acute Kidney Injury

AKI does not look exactly the same in every person. Some people have few noticeable symptoms, while others become seriously ill.

Possible signs include:

Producing less urine than usual
Swelling in the legs, ankles, feet, or around the eyes
Unusual tiredness or weakness
Nausea or vomiting
Shortness of breath, particularly when excess fluid affects the lungs
Confusion or difficulty concentrating
Changes in blood pressure
Loss of appetite
Fluid retention

A major reduction in urine output should not be ignored, particularly when it occurs together with swelling, breathing problems, weakness, confusion, or severe illness.

Can AKI Happen Without Symptoms?

Yes.

One of the important features of AKI is that symptoms may not clearly reveal how much kidney function has changed. Healthcare professionals may identify AKI through laboratory testing, particularly changes in serum creatinine and other measurements.

This is one reason kidney function testing can be important in people who are seriously ill or who have risk factors for kidney injury.

How Is Acute Kidney Injury Diagnosed?

Doctors do not diagnose AKI from symptoms alone. They consider the person's medical history, examination, urine output, laboratory results, medications, and possible causes.

Tests may include:

Blood Tests

Blood testing can measure:

Serum creatinine
Blood urea nitrogen (BUN)
Potassium and other electrolytes
Acid-base status when appropriate

A rise in creatinine can indicate a decline in kidney filtration, although the result must be interpreted in the context of the individual's baseline kidney function and clinical situation.

Urine Testing

Urinalysis and other urine studies can provide clues about possible kidney injury or its cause.

Imaging

When urinary obstruction is suspected, kidney or abdominal ultrasound may help identify a blockage. Other imaging studies may be considered depending on the clinical situation.

Medication Review

Healthcare professionals may review prescription medicines, over-the-counter drugs, supplements, and other exposures because some substances can contribute to kidney injury.

How Is AKI Treated?

There is no single treatment that works for every case of AKI.

The most important step is identifying and addressing the underlying cause.

Treatment may involve:

Correcting dehydration or abnormal fluid status when appropriate
Treating infections or other underlying illnesses
Managing blood pressure and circulation
Addressing urinary obstruction
Reviewing potentially kidney-harming medications
Adjusting medication doses when kidney function has changed
Managing abnormal potassium or acid levels
Controlling excess fluid
Monitoring kidney function and urine output

Treatment decisions must be individualized. Giving additional fluid is not automatically appropriate for every person with AKI because some patients may already have excess fluid.

When Is Dialysis Needed?

Dialysis is not required for every person with AKI.

In severe cases, temporary kidney replacement therapy may be considered when the kidneys cannot adequately manage dangerous complications. Depending on the clinical situation, this can include severe electrolyte abnormalities, significant fluid accumulation, or substantial buildup of waste products.

MedlinePlus notes that dialysis can be lifesaving in certain severe cases, including dangerously high potassium or major fluid and waste accumulation.

Whether dialysis is needed, when it should begin, and how long it should continue are decisions made by the treating medical team.

Possible Complications of AKI

Severe AKI can affect several systems in the body.

Potential complications include:

High potassium levels
Fluid overload
Metabolic abnormalities
Abnormal heart rhythms associated with severe electrolyte disturbances
Breathing difficulty from excess fluid
Confusion or other changes in mental status
Need for dialysis
Increased risk of future kidney problems

AKI can also be associated with longer-term kidney disease in some people, which is why follow-up after an episode can be important. NIDDK identifies AKI as one of the conditions associated with later chronic kidney disease.

Is Acute Kidney Injury Reversible?

Sometimes, yes.

Recovery depends heavily on:

The cause of AKI
How severe the injury is
How quickly the underlying problem is treated
Whether other organs are affected
The person's previous kidney health
Whether complications develop

Some people recover much of their kidney function, while others may have persistent kidney impairment.

For this reason, recovery should not simply be assumed because symptoms improve. Follow-up testing may be needed to determine how well the kidneys have recovered.

Who May Be at Higher Risk?

The risk of AKI can increase in people experiencing serious illness, major fluid loss, infection, low blood pressure, surgery, or other conditions that affect circulation or kidney function.

People with existing kidney problems may also require particular attention when exposed to situations or medications that can further stress the kidneys.

Can Acute Kidney Injury Be Prevented?

Not every case of AKI can be prevented, but some risks can be reduced.

Helpful steps include:

Stay Alert to Significant Fluid Loss

During illness involving substantial vomiting, diarrhea, fever, or other fluid loss, contact a healthcare professional when appropriate rather than assuming that drinking large amounts of fluid is always the correct solution.

Manage Chronic Health Conditions

Conditions such as diabetes and high blood pressure can affect long-term kidney health. Appropriate management can help protect kidney function.

Review Medicines With a Healthcare Professional

Do not stop prescribed medication on your own. Instead, ask a healthcare professional or pharmacist whether your medications require adjustment during significant illness or changes in kidney function.

Be Careful With Kidney-Stressing Substances

Some medicines and other substances can contribute to kidney injury. Medication decisions should be individualized, especially when kidney function is already reduced.

Treat Serious Infections Promptly

Severe infections can contribute to AKI. Prompt medical evaluation is particularly important when an infection is accompanied by severe weakness, confusion, breathing difficulty, very low blood pressure, or other concerning symptoms.

AKI vs. Chronic Kidney Disease: What's the Difference?

The terms can sound similar, but they describe different patterns.

Acute kidney injury develops suddenly, often over a short period.

Chronic kidney disease (CKD) develops over a longer period and involves persistent abnormalities in kidney structure or function.

AKI can sometimes contribute to future chronic kidney problems, so people who have experienced AKI may need appropriate follow-up.

When Should You Seek Urgent Medical Attention?

Do not wait for a routine appointment if you develop potentially serious symptoms such as:

Very little or no urine
Severe or rapidly increasing swelling
Significant difficulty breathing
New confusion or a major change in alertness
Severe weakness during a serious illness
Symptoms suggesting a serious infection
Other rapidly worsening symptoms

These symptoms can have many possible causes, but some require urgent evaluation.

Key Takeaways

Acute kidney injury is a sudden reduction in kidney function that can occur because of reduced blood flow, direct kidney injury, or urinary obstruction.

The most important points are:

AKI can occur suddenly and may initially cause few symptoms.
Reduced urine output can be an important warning sign.
Blood tests, urine testing, medical history, and sometimes imaging help identify AKI and its cause.
Treatment focuses on correcting the underlying problem and managing complications.
Dialysis is needed only in some severe cases.
Recovery varies from person to person.
Follow-up may be important because AKI can increase the risk of future kidney problems.

Frequently Asked Questions

Is acute kidney injury the same as acute renal failure?

The terms are related. Acute kidney injury (AKI) is now the preferred broader clinical term, while “acute renal failure” is an older term that is still encountered in some educational materials and medical records.

Can dehydration cause AKI?

Severe dehydration or fluid loss can reduce blood flow to the kidneys and contribute to AKI. The appropriate treatment depends on the cause and the person's overall medical condition.

Does AKI always require dialysis?

No. Many people with AKI do not require dialysis. Dialysis may be used when severe complications cannot be adequately controlled by other measures.

Can kidney function recover after AKI?

Recovery is possible, but it varies depending on the cause and severity of the injury and the person's overall health.

What test is commonly used to monitor kidney function during AKI?

Serum creatinine is an important laboratory measurement used to assess kidney function, along with urine output and other laboratory findings.

Acute Kidney Injury (AKI): Symptoms, Causes, Treatment & Prevention