Acute kidney injury refers to a sudden decline in kidney function that causes waste products to accumulate in the body. It may manifest as symptoms of weakness, confusion, and less frequent urination.

The condition is very serious and requires people to receive treatment promptly. Treatment might involve blood pressure medications and temporary dialysis — a procedure that cleans the blood of wastes.

Acute kidney injury (AKI) most often affects critically ill individuals already admitted to a hospital.

According to StatsPearls, 1% of people admitted to a hospital in the United States may experience it. During hospitalization, the incidence ranges from approximately 2–5%, but AKI can occur in up to 67% of those in an intensive care unit (ICU).

Keep reading to learn more about acute kidney injury, including the symptoms, diagnosis, and outlook for this condition.

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Acute kidney injury refers to a sudden and frequently reversible decline in kidney function. It can happen within a few hours to a few days. People should not confuse AKI with blunt trauma to the organ as AKI involves the kidney’s microanatomy, such as blood vessels.

Doctors use the KDIGO classification to define AKI. KDIGO stands for Kidney Disease Improving Global Outcomes, and it defines acute kidney injury in terms of creatinine — a waste product the muscles make or urine volume — and involves:

  • increases in serum creatinine greater than or equal to 0.3 milligrams per deciliter within 48 hours
  • increases in serum creatinine greater than or equal to 1.5 times the baseline, which has occurred within the prior 7 days
  • urine volume less than 0.5 milliliters/kilogram/hour for 6 hours

The condition causes an accumulation of waste products in the blood and makes it difficult for the kidneys to maintain a healthy fluid balance in the body. It is very serious and requires prompt treatment to prevent permanent kidney damage.

Early treatment enables most people’s kidney function to return to normal or close to normal. However, if the condition causes severe damage, it can lead to chronic kidney disease. Over time, this can result in kidney failure called end-stage kidney failure.

There are four main stages of AKI:

  • Stage 1, Initiation: The condition begins, but a person may not experience any symptoms at this stage.
  • Stage 2, Oligo-anuria: A person may begin to experience symptoms of kidney dysfunction, one of which, includes urinating less frequently. Less urine output can cause fluid retention, accumulation of waste products, high blood pressure, and even heart failure.
  • Stage 3, Polyuria: A person’s kidney function slowly restores. However, they may still experience substantial losses of water, and electrolytessodium and potassium mainly. Low potassium may lead to heart arrhythmias, or irregular heart rhythms.
  • Stage 4, Restitution: Kidney function restores.

If the process of recovery from AKI takes more than 3 months, the person may develop chronic kidney disease.

Critically ill people in an ICU have the highest risk of developing AKI. Some people that have an increased likelihood of developing this condition include those:

AKI can occur for three main reasons.

Reduced blood flow

Reasons for reduced blood flow to the kidneys can include:

Direct damage to the kidneys

Causes can include:

  • multiple myeloma, a cancer that affects plasma cells, a type of white blood cells
  • sepsis, a life threatening response to an infection
  • vasculitis, a rare condition that causes scarring and inflammation in the blood vessels
  • scleroderma, a group of diseases that involve the connective tissue supporting internal organs
  • interstitial nephritis, a condition that entails the swelling of the spaces between small kidney tubules caused by an allergic reaction to certain medications
  • conditions that produce damage and inflammation in the tubules, filtering units, or small blood vessels of the kidneys, such as glomerulonephritis, which affects the filtering part of the kidneys

Blockage of the urinary tract

Causes may include:

People with a milder case of AKI may not have any symptoms, whereas people with more severe cases might experience symptoms, including:

Additionally, AKI can affect other organs, including the lungs, heart, and brain.

The diagnostic process has several parts. It involves a physical exam and medical history to note symptoms and their timeline of progression. This includes reviewing medications to determine if their side effects are a factor.

The exam also entails checking other organs for symptoms that may indicate the cause. For example, a rash may suggest vasculitis and certain eye problems may indicate diabetes.

A diagnosis also necessitates some or all of the following tests:

  • Basic metabolic panel: This blood test measures waste products the kidney removes from the blood, along with glucose and electrolytes, such as sodium and potassium.
  • Glomerular filtration rate (GFR): This blood test helps estimate any reduction in kidney function.
  • Urinalysis: This measures protein, electrolytes, and other substances in the urine.
  • Urine output measurement: This involves tracking the amount of urine a person passes daily.
  • Imaging: A CT scan and ultrasound provide pictures of the kidney’s structure and may be helpful.
  • Kidney biopsy: While uncommon, doctors use this to help identify a cause when multiple conditions are a possibility. It can help a doctor diagnose the cause more quickly, leading to a more prompt and effective treatment.

Treatment can vary with the cause and severity of the condition and may include:

  • medications to adjust electrolytes and control blood pressure
  • medications, such as diuretics, to maintain a healthy amount of body fluid by eliminating excess fluid through urine
  • temporary dialysis for people with severe AKI
  • diet changes, which involve restricting fluid, salt, and foods high in potassium

Complications include:

  • high potassium levels, which may lead to an irregular heartbeat
  • metabolic acidosis, which is the inability to eliminate acids from the body
  • swelling in the lungs from fluid overload
  • cardiovascular disease, such as heart failure from fluid overload
  • neurological problems, such as a decline in a person’s ability to think clearly
  • gastrointestinal problems, such as bleeding and vomiting

Outcomes depend on:

  • the cause of AKI
  • the duration of dysfunction
  • the presence of underlying kidney disease

When AKI is chronic, at least 12–15% of people require permanent dialysis.

The in-hospital death rate ranges from 30–50%, particularly among those who need dialysis. Factors that can complicate a person’s outlook include:

  • being of advanced age
  • producing only very small amounts of urine
  • needing blood transfusions
  • using drugs that constrict blood vessels
  • having low blood pressure
  • having dysfunction in multiple organs

The Centers for Disease Control and Prevention (CDC) does not have prevention recommendations specific to AKI, but it does offer healthy kidney tips. These include:

  • controlling risk factors, such as diabetes and high blood pressure
  • following a doctor’s instructions for taking medications
  • quitting smoking
  • maintaining a healthy weight
  • getting regular exercise
  • eating more fruits and vegetables
  • avoiding foods with high salt quantities
  • getting kidneys checked during doctor checkups

A person who has risk factors for the condition may wish to discuss the medications they take with a doctor.

Acute kidney injury is a sudden reduction in kidney function, which can occur within a few hours to a few days. It can hinder healthy fluid balance in the body.

Symptoms may not manifest in people with mild cases, but symptoms in people with severe cases can be life threatening, such as seizures and coma. Early treatment is vital, as it enables most people’s kidney function to return to normal.

Once serious damage occurs, the outlook is not good. As such, people should take preventative measures and seek immediate treatment once symptoms begin.