What is acute kidney injury?

Acute kidney injury — often called AKI, or sometimes "acute renal failure" — is when your kidneys suddenly stop working properly, usually over hours to days. This is different from chronic kidney disease, which develops slowly over years.

The word "acute" means sudden. And while that sounds alarming, AKI is actually one of the few kidney conditions that can sometimes be fully reversed — if caught and treated quickly.

AKI is a medical emergency. If you or someone you know has signs of sudden kidney failure — especially very little or no urine, extreme swelling, or confusion — seek emergency care immediately.

What causes AKI?

There are three main categories of causes:

Before the kidney (pre-renal)

The kidneys aren't getting enough blood flow. This is the most common cause of AKI. It can happen from severe dehydration, heavy blood loss, heart failure, or extreme low blood pressure (septic shock).

Within the kidney (intrinsic renal)

Direct damage to kidney tissue. Common causes include:

  • Certain medications — including NSAIDs, some antibiotics (gentamicin), contrast dye used in CT scans, and some chemotherapy drugs
  • Infections that reach the kidney
  • Inflammation inside the kidney (nephritis)
  • Blockage of blood vessels in the kidney

After the kidney (post-renal)

A blockage preventing urine from leaving the kidney — such as kidney stones, an enlarged prostate, or a tumor pressing on the urinary tract.

What are the symptoms?

Symptoms of AKI come on quickly and can include:

  • Dramatically reduced urine output — or no urine at all
  • Severe swelling in legs, ankles, and around the eyes
  • Shortness of breath (from fluid buildup around the lungs)
  • Extreme fatigue and weakness
  • Confusion or difficulty thinking clearly
  • Nausea and vomiting
  • Chest pain or pressure
  • Irregular heartbeat (from high potassium levels)

In some cases — particularly when AKI develops during a hospital stay — there are no obvious symptoms and it's detected only through blood tests showing a sudden rise in creatinine.

How is AKI treated?

Treatment depends entirely on the cause. The first priority is identifying and removing whatever is causing the injury.

If caused by dehydration: IV fluids to restore blood volume and pressure to the kidneys.
If caused by a medication: Stopping the offending drug immediately.
If caused by a blockage: Removing the blockage — through a catheter, stent, or surgery.
If caused by infection: Antibiotics to treat the underlying infection.
If severe: Temporary dialysis to take over kidney function while the kidneys recover.
Many people recover fully from AKI, but some are left with permanent kidney damage. Having AKI also significantly raises your risk of developing CKD later in life — which is why follow-up kidney monitoring after an AKI episode is so important.