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

Kidney problems can develop suddenly or over a long period of time. The rapid loss of kidney function is called acute kidney injury (AKI). It is typically due to an event like dehydration, blood loss, or a urinary tract obstruction.

The gradual loss of kidney function is referred to as chronic kidney disease (CKD) and is typically caused by a long-term condition like diabetes or high blood pressure. In some people, CKD can lead to end-stage renal disease, in which the kidneys completely cease functioning.

Because the treatment of AKI and CKD differ, it is important to identify the underlying cause based on a review of your symptoms and medical history and a panel of lab and imaging tests.

An imaging technician performing a kidney ultrasound

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This article describes the differences between acute kidney failure and chronic kidney disease, including the distinct causes, symptoms, treatments, and outcomes.

Difference Between Acute Kidney Injury and Chronic Kidney Disease 

The kidneys function as the body's filtration system. These bean-shaped organs, which are about the size of a fist, remove waste and excess fluid from the body through urine. They also maintain a stable balance of salt, potassium, and acids in the body and produce renin, a hormone that helps regulate blood pressure and other body functions.

Many conditions, diseases, and medicines can affect the kidneys and create situations that lead to acute and chronic kidney problems. The term acute is used when the onset of symptoms is sudden and a significant change from normal. The term chronic is used when the problem is long-developing and persistent.

Acute kidney injury (AKI) and chronic kidney disease (CKD) differ in several key ways:

  • With AKI, everything occurs suddenly and sometimes severely. The cause is usually related to a drug, illness, or injury that steeply decreases the function of the kidneys (as measured by blood tests called the renal function panel). The symptoms, in turn, will develop suddenly and severely. In most cases, AKI can be reversed once the underlying condition is treated.
  • With CKD, everything progresses gradually. The cause is mainly due to chronic illnesses like diabetes or high blood pressure that progressively damage the kidneys. Because the decline is gradual, the symptoms are often not apparent until the kidney damage is severe. CKD is not reversible but can be managed to preserve kidney function.
AKI
  • Usually caused by a medication, illness, or injury

  • The decline in kidney function is steep

  • The onset of symptoms is sudden and can be severe

  • The treatment is focused on resolving the underlying cause

  • The condition is most often reversible

CKD
  • Usually caused by a chronic illness

  • The decline in kidney function is gradual

  • Symptoms may not appear until the damage is severe

  • The treatment is focused on managing the underlying cause

  • The condition is generally non-reversible

Acute Kidney Injury

Acute kidney injury (formerly known as acute kidney failure) is the sudden decrease in kidney function that develops within seven days. This is evidenced by a decrease in urine output and/or an increase of a waste product called creatinine in blood tests.

AKI is seen in 10% to 15% of people admitted to the hospital and more than 50% of people admitted to an intensive care unit (ICU).

Causes

The causes of AKI are many and differ by whether the problem occurs above the kidneys (prerenal AKI), in the kidneys (intrinsic AKI), or below the kidneys (postrenal AKI).

Prerenal AKI is characterized by the reduced flow of blood to both kidneys. This may be due to an obstruction of a blood vessel servicing the kidneys or a steep drop in blood pressure (reducing the volume of blood reaching the kidneys). Causes of prerenal AKI include:

  • Heart attack (blocked blood flow to the heart muscle)
  • Heart failure (the heart does not pump enough blood for the body's needs)
  • Hypovolemia (the reduction of fluid volumes due to severe dehydration, blood loss, or burns)
  • Liver failure (which can indirectly impede blood flow to the kidneys)
  • Renal artery thrombosis (a blood clot in an artery servicing the kidneys)
  • Sepsis (the spread of a local infection throughout the body that can trigger a drop in blood pressure)

Intrinsic AKI is caused by agents, diseases, or conditions directly affecting one or more structures of the kidneys themselves. These include:

Postrenal AKI is characterized by the downstream obstruction of urine from the kidneys. Causes include:

AKI is generally caused by multiple conditions that together cause a rapid decline in kidney function. An example includes severe dehydration in someone taking medications toxic to the kidneys.

Symptoms 

When AKI symptoms occur, they tend to develop rapidly, causing a cascade of potentially severe symptoms, including:

AKI will sometimes cause no symptoms and only be detected with lab tests while a person is hospitalized or being seen for another medical condition.

AKI can lead to potentially severe complications, including pulmonary edema (excess fluid in the lungs) and hyperkalemia (dangerously high blood potassium levels). If left untreated, the rapid buildup of toxins can also lead to respiratory failure, life-threatening heart rhythm disturbances, and death.

Treatment

The treatment for AKI typically requires a hospital stay. With that said, most people who get AKI are already hospitalized for a condition that contributes to the onset of AKI.

While the treatment is largely focused on resolving the underlying cause, efforts will be made to prevent complications of AKI. This may include:

  • Intravenous fluids (delivered through a needle into the bloodstream to increase fluid volumes in people with hypovolemia)
  • Diuretics (used to reduce excess fluids in the lungs, legs, or feet)
  • Intravenous calcium (used to normalize potassium levels in people with severe hyperkalemia)
  • Hemodialysis (a blood filtration system used to clear toxins from the blood)

While most cases of AKI can be reversed once the underlying condition is treated, some injuries can cause permanent damage that leads to chronic kidney disease and long-term kidney failure.

Chronic Kidney Disease

Chronic kidney disease (CKD) is characterized by the gradual loss of kidney function over a period of months or years. CKD affects 1 of every 7 adults in the United States or roughly 37 million people. Of these, only 1 in 10 are aware that they have kidney disease.

Causes

Most cases of CKD are caused by three conditions that either directly or indirectly affect the internal structure of the kidneys:

  • High blood pressure (which can cause the hardening and narrowing of the blood vessels servicing the kidneys)
  • Diabetes (in which high blood sugar levels can progressively damage the filters of the kidneys, called glomeruli)
  • Glomerulonephritis (the inflammation of glomeruli caused by many different conditions, including bacterial infections like strep throat, viral diseases like hepatitis C, and autoimmune disorders like lupus or IgA nephropathy)

Other causes include recurrent pyelonephritis (kidney infection usually caused by bacteria) and interstitial nephritis (inflammation of the tubules of the kidneys).

On occasion, CKD may be caused by reflux nephropathy (the backflow of urine into the kidneys), polycystic kidney disease (a genetic disorder that causes the formation of cysts in the kidneys), or drugs or toxins that can permanently damage the kidneys.

Symptoms 

The appearance of symptoms in people with CKD can be so gradual that they don't realize they have the disease until it is advanced. In fact, only 1 of every 2 people with severe CKD (less than 30% kidney function) realizes that they have it.

As the kidney function decreases, more overt symptoms of CKD may develop, including:

  • Persistent fatigue and weakness
  • Ammonia-smelling breath
  • Poor appetite
  • Dry, itchy skin
  • Swollen feet and ankles due to fluid overload
  • Puffy eyes, especially in the morning
  • Needing to urinate frequently
  • Frequent nighttime urination
  • Trouble sleeping
  • Muscle cramps at night
  • Difficulty concentrating

Over time, CKD can lead to complications such as anemia, heart disease, weak bones, reduced fertility, seizures, and an increased risk of infections. Depression, anxiety, and cognitive impairment can be found in people with CKD.

People with advanced CKD may also develop abnormally high blood phosphate levels, called hyperphosphatemia, which can increase the risk of muscle and bone damage.

CKD can also cause pregnancy complications, including preterm birth, low birth weight, and preeclampsia (a potentially dangerous condition characterized by high blood pressure).

Treatment

There is no cure for CKD, but there are treatments that can preserve kidney function and slow the progression of the disease. This starts with the identification and management of the underlying cause.

Among the treatments used to manage CKD are:

  • High blood pressure medications, such as ACE inhibitors
  • Cholesterol medications, like statins (used to prevent the buildup of plaque in renal arteries)
  • Diuretics (used to reduce fluid retention and maintain the balance of fluids in the body)
  • Erythropoietin-stimulating agents (used to treat anemia by stimulating a hormone called erythropoietin that increases red blood cell production)
  • Vitamin D supplements (used to help strengthen bones and reduce the risk of fractures)
  • Phosphate binders (used to reduce the absorption of phosphates and the risk of hyperphosphatemia)
  • Low-protein diets (used to minimize the buildup of waste products caused by the breakdown of dietary protein)

People with end-stage kidney disease (less than 15% kidney function) require either dialysis or a kidney transplant to stay alive.

Summary

There are many conditions that can reduce the function of the kidneys either suddenly or gradually. Acute kidney injury (AKI) occurs when the kidneys suddenly fail due to an injury, medication, or illness. Chronic kidney disease (CKD) is the gradual loss of kidney function mainly caused by high blood pressure, diabetes, and an inflammatory condition known as glomerulonephritis.

AKI and CKD also differ in their symptoms and treatment. AKI tends to cause sudden, severe symptoms that are easily recognized, while CKD symptoms develop slowly and are easily mistaken for other conditions. While AKI can usually be reversed by resolving the underlying cause, CKD is not reversible and need to be managed to preserve the function of the kidneys.

A Word From Verywell

The early treatment of kidney disease will almost invariably improve outcomes, whether you have AKI or CKD. With CKD, however, the symptoms are often "invisible" until the kidneys are severely and irreparably damaged.

To this end, it is important to identify your risk factors for CKD and speak with your healthcare provider about screening you for CKD if you are at risk. All it takes is a simple panel of blood tests to determine if your kidneys are functioning normally or not.

The National Kidney Foundation and other professional organizations currently recommend CKD screening for at-risk groups, including adults over 60, people of color, and people with diabetes, high blood pressure, or a family history of kidney disease.

Frequently Asked Questions

  • What’s the main difference between acute kidney failure and chronic kidney disease?

    Acute kidney injury (AKI) causes sudden and severe symptoms that are usually reversible. By contrast, chronic kidney disease (CKD) progresses slowly and is generally non-reversible, causing symptoms that are often only noticed when the kidney damage is severe.

  • What are some causes of acute kidney injury?

    The three main causes of acute kidney injury are:

    • A sudden drop in blood flow to the kidneys due to blood or fluid loss, heart problems, organ failure, and other causes
    • Direct kidney damage caused by trauma, infections, inflammatory conditions, certain medications, and other causes
    • A sudden blockage of urine flow due to kidney or bladder stones, a blocked urinary catheter, bladder or prostate cancer, and other causes
  • Is chronic kidney disease curable?

    There is no cure for chronic kidney disease, but treatments are available that can help relieve symptoms and stop the disease from getting worse.

  • How do I know if I have chronic kidney disease?

    You often don't. Only 1 in 10 people in the United States are aware that they have chronic kidney disease (CKD). For this reason, CKD screening should be sought if you are over 60 or have high blood pressure, diabetes, or a family history of kidney disease.

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