What Is Acute Kidney Failure? Everything To Know

Acute kidney failure, now known as acute kidney injury (AKI), occurs when your kidneys suddenly lose their ability to filter waste products from your blood. This rapid decline in kidney function can happen within a few hours or days, causing swelling in the legs, fatigue, shortness of breath, reduced appetite, and little to no urination, among other symptoms. 

There are many causes of acute kidney injury, including underlying conditions that reduce blood flow to the kidneys, infections, substance use, and serious health events, such as severe burns or allergic reactions. Acute kidney failure requires immediate treatment to prevent permanent long-term kidney damage. Treatment options like medications, dialysis, and lifestyle changes can help preserve kidney function and prevent complications. 

Acute Kidney Injury Symptoms

Symptoms of acute kidney injury (AKI) vary depending on the underlying cause, how rapidly kidney function declines, and the severity of the condition. Milder forms of AKI may only cause symptoms once the condition progresses. When symptoms develop, they may include: 

• Urinating less often than usual 
• Swelling in the legs, ankles, and feet 
• Fatigue and weakness
• Confusion 
• Mood changes
• Reduced appetite 
• Nausea 
• Flank pain (on the side of your body between the ribs and hips) 
• Chest pain or heaviness 
• Seizures 

What Causes AKI?

Acute kidney failure occurs when the kidneys suddenly lose their ability to filter waste products from the blood. This rapid decline in function typically happens due to reduced blood flow to the kidneys, damage to the kidney tissues, or blockage preventing urine from leaving the kidneys. Healthcare providers categorize AKI causes as prerenal, renal, or postrenal, depending on the underlying problem.

Prerenal Causes 

Prerenal refers to circumstances that reduce blood flow to the kidneys, making it difficult for them to filter waste effectively. Prerenal causes of AKI include: 

• Excessive nonsteroidal anti-inflammatory drug (NSAID) use, such as Advil (ibuprofen) and Aleve (naproxen)
• Heart disease
• Heart attack
• Hemorrhage (severe blood loss) 
• Persistent diarrhea or vomiting
• Liver failure
• Low blood pressure
• Dehydration 
• Severe skin burns
• Anaphylaxis (life-threatening allergic reaction) 

Renal Causes

Renal causes of AKI include conditions or substances that cause direct damage to the kidney tissue, impairing normal kidney function. These causes include: 

• Kidney diseases, such as lupus nephritis or glomerulonephritis 
• Certain medications, including chemotherapy drugs, some antibiotics, and iodine-based contrast dyes for computed tomography (CT) scans 
• Substance use disorder
• Infections, such as sepsis and COVID-19
• Blood clots in the kidneys 
• Blood vessel disorders, such as vasculitis 

Postrenal Causes

Postrenal causes block the normal flow of urine in the ureters—the tubes that carry urine from the kidneys to the bladder—preventing it from leaving the kidneys. Common postrenal causes of AKI include:  

• Kidney stones
• Enlarged prostate 
• Tumors 
• Blood clots or cholesterol (fat) in or around kidney blood vessels 

Risk Factors 

Acute kidney injury is most common in people receiving care in the hospital due to serious illness or recovering from surgery. This type of kidney failure affects nearly 25% of people admitted to hospitals and up to 60% of those receiving critical care. 

In addition to hospitalization for major surgery or illness, several factors can increase the risk of AKI, including: 

• Being over the age of 65
• Undergoing major surgery, such as a bypass surgery
• Living with underlying health conditions like kidney disease, diabetes, high blood pressure, heart disease, and chronic obstructive pulmonary disease (COPD)

Diagnosis

Diagnosing acute kidney injury (AKI) involves reviewing your medical history, a physical examination, and diagnostic tests to assess kidney function. The diagnostic process helps determine the underlying cause of AKI and informs providers on what treatment options they can offer you.

Your healthcare provider will begin by reviewing your medical history to determine your risk factors for AKI.  They will ask about any recent injuries, illnesses, or surgeries and inquire about your water intake, current medications, and substance use. During the physical examination, they will ask about your symptoms and look for signs of AKI, such as swelling in your legs, ankles, and feet. 

Diagnostic tests are necessary for accurately diagnosing AKI. These tests assess kidney function and help identify the cause of AKI. Your healthcare provider may order tests such as:

• Blood urea nitrogen (BUN): Measures the amount of urea nitrogen in your blood—a waste product that forms when protein breaks down in the body. Elevated BUN levels can indicate impaired kidney function or dehydration.
• Creatinine clearance: Assesses how well your kidneys filter creatinine, a waste product of muscle metabolism. It requires collecting your urine over 24 hours and a blood draw at the end of this period to compare creatinine levels in your urine and blood.
• Other blood tests: Check the balance of electrolytes in your bloodstream, such as potassium, sodium, and calcium, which can become imbalanced due to kidney dysfunction.
• Urinalysis (urine test): Detects signs of kidney problems, such as blood in urine, protein, or abnormal levels of waste products, which can indicate infection, damage, or kidney blockages.
• Imaging scans: Uses ultrasound and computed tomography (CT) scans to allow healthcare providers to visualize the kidneys and urinary tract to identify abnormalities like blockages, kidney stones, or structural problems. 
• Biopsy: Remove a small sample of kidney tissue to examine under a microscope and identify the cause of AKI. However, this typically occurs in rare cases.

Stages of Acute Kidney Injury 

After evaluating your test results, your healthcare provider will stage your acute kidney injury (AKI). Healthcare providers determine the stage of AKI based on serum creatinine levels and urine output. There are three stages, which include:

• Stage 1: Mild decrease in kidney function with a slight rise in serum creatinine levels or reduced urine output. Early detection at this stage can often lead to quick recovery with proper treatment.
• Stage 2: Moderate kidney impairment, with a more significant rise in creatinine levels and a noticeable reduction in urine output. 
• Stage 3: Severe loss of kidney function, with critically elevated creatinine levels or little to no urine output. This stage may require dialysis or other aggressive treatments to support the kidneys and prevent complications.

Acute Kidney Injury Treatments  

Treatment for acute kidney failure aims to restore normal kidney function and prevent complications, such as permanent kidney damage. Treatment strategies focus on supporting kidney function until they recover to reduce the buildup of waste in the body. In many cases, AKI is reversible if treated promptly, but in severe cases, more intensive interventions may be necessary.

You may require treatment in the hospital until your kidneys heal, depending on the stage and severity of AKI. Common treatment approaches include: 

• Stopping medications: If you take medicines that contribute to AKI or are potentially harmful to the kidneys, you may need to stop taking them while your kidneys heal. 
• Fluid replacement: Restoring fluids and electrolytes can improve blood flow to the kidneys. This may require drinking more water or receiving fluids intravenously (IV) through a vein. 
• Medications: Antibiotics treat underlying infections contributing to AKI. Diuretics (water pills) help increase urine output, and afterload-reducing medications can help dilate (widen) blood vessels to improve blood flow to the kidneys. 
• Catheterization: If a blockage in the urinary tract is causing AKI, you may need a catheter (tube) to drain your bladder. 
• Dialysis: In severe cases, you may need dialysis, which involves using a machine to filter waste and fluids from the blood while your kidneys heal.

How To Prevent AKI

It is not always possible to prevent acute kidney injury (AKI). However, certain lifestyle habits can help protect kidney health and lower the risk of AKI. To prevent AKI or reduce the risk of recurrence, consider the following tips:

• Eat a healthy, well-balanced diet with plenty of fruits, vegetables, and low-sodium (salt) foods
• Stay hydrated to help improve kidney function and prevent kidney stones
• Exercise regularly 
• Quit smoking
• Maintain a body weight that's right for you
• Manage underlying conditions by following your treatment plan 
• Limit alcohol intake 
• Get regular check-ups with a healthcare provider and blood tests to assess kidney function, especially if you have risk factors for AKI

Complications 

Untreated acute kidney injury can lead to serious complications. These complications develop when kidneys cannot perform their essential function, causing waste products to build up in the body. Possible complications include: 

• Chronic kidney disease (CKD): AKI can lead to permanent kidney damage, which can cause CKD and lead to long-term issues with filtering waste
• Fluid overload: When the kidneys cannot remove excess fluid, it can accumulate in the body, leading to swelling and potentially life-threatening conditions like pulmonary edema (fluid in the lungs)
• Metabolic acidosis: Occurs when the kidneys cannot remove enough acid, leading to a lowered pH in the blood and symptoms like rapid breathing, fatigue, and confusion
• Electrolyte imbalances: AKI can cause dangerous levels of potassium, sodium, or calcium in the blood, which can affect heart function and lead to irregular heartbeats (known as arrhythmias)

A Quick Review

Acute kidney injury (AKI), or acute kidney failure, is a sudden decline in kidney function that can lead to dangerous levels of waste buildup in the body. Symptoms of AKI include peeing less often than usual, swelling, fatigue, nausea, and flank pain. Early diagnosis and treatment of AKI are essential for preventing complications like permanent kidney damage. Depending on the stage of AKI, treatment may include fluid replacements, medications, or dialysis.