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

Written by: Editorial Team

Medically reviewed by: Dr. A Kishore Kumar - Consultant Nephrologist and Renal Transplant Physician

Overview | Epidemiology | Types | Symptoms | Causes | Risk Factors | Complications | Diagnosis | Treatment | Prevention | Acute kidney injury vs Chronic kidney disease | FAQs | When to consult a Doctor

Acute kidney injury definition

Acute kidney injury (AKI) is defined as a sudden decline in kidney function that develops over hours to days, leading to the buildup of waste products, electrolytes, and excess fluid in the body. It may present with reduced urine output, swelling of the legs or face, fatigue, nausea, confusion, shortness of breath (SOB), or chest discomfort due to fluid overload.

Common causes are severe dehydration, major infections (sepsis), heart failure, low blood pressure, urinary tract obstruction, certain medications (such as some antibiotics or pain relievers), and exposure to contrast dye. If left untreated, AKI can result in serious complications like electrolyte imbalance (high potassium), metabolic acidosis, fluid overload affecting the lungs, progression to chronic kidney disease, or even life-threatening cardiac arrhythmias (abnormal heart rhythm).

Management is usually led by a nephrologist along with critical care specialists in an intensive care unit (ICU), aiming to treat the underlying cause, stabilise fluids and electrolytes, and initiate dialysis when required.

AKI is a common and serious condition worldwide. Studies show that AKI affects about 10–20% of hospitalized patients and up to 30–50% of patients in intensive care units (ICUs). Globally, it is estimated that more than 130 lakh people develop AKI each year, with nearly 17 lakh deaths annually, especially in low- and middle-income countries. In high-income countries, AKI usually affects hospitalised patients due to sepsis, major surgery, or medications. In developing regions, it is linked to infections, dehydration, obstetric complications, and toxins.

In India, AKI is common and remains a major cause of hospital-related illness and death. Studies show that AKI occurs in about 5–7% of hospitalized patients and in 30–40% of ICU patients. In India, sepsis is the leading cause of AKI, especially in critically ill patients. Community-acquired AKI is frequently caused by dehydration, infections, snake bites, obstetric complications, and nephrotoxic drugs, while hospital-acquired AKI is linked to sepsis, major surgeries, and contrast exposure. Mortality in severe AKI cases may range from 20–50%, particularly when dialysis is required. 

Acute kidney injury is classified into three main types based on the underlying cause and where the problem occurs in relation to the kidneys. The following are the types of acute kidney injury:

• Prerenal acute kidney injury
• Intrarenal (intrinsic) acute kidney injury 
• Postrenal acute kidney injury

This type occurs when there is a reduction in blood flow to the kidneys without direct structural damage. Because the kidneys depend on an adequate blood supply to filter waste, any condition that decreases circulation—such as dehydration, severe blood loss, heart failure, low blood pressure, or sepsis—can impair kidney function. The kidney tissue itself is initially normal, and function often improves once blood flow is restored. 

This type develops due to direct damage to the kidney structures, including the tubules, glomeruli, blood vessels, or interstitial tissue. Causes include prolonged reduced blood flow, severe infections, toxins, certain medications, autoimmune disorders, or acute tubular necrosis. 

This type occurs when there is an obstruction to urine flow after it leaves the kidneys. Blockages increase pressure within the urinary system and impair kidney filtration. Common causes are enlarged prostate, kidney stones, tumors, or ureteral strictures.

Acute kidney injury is a sudden decline in kidney function that can range from mild to life-threatening. Symptoms may develop over hours to days, and sometimes are subtle in the early stages. Common signs and symptoms of acute kidney injury include:

• Oliguria (reduced urine output)
• Swelling in the legs, ankles, face, or around the eyes
• Shortness of breath
• Fatigue and weakness
• Nausea, vomiting, and loss of appetite
• Chest pain or pressure 
• High blood pressure
• Confusion or mood changes
• Flank pain

Oliguria (reduced urine output):  In acute kidney injury, the kidneys lose their ability to filter blood and produce urine effectively. As kidney function declines, urine output decreases because waste products and excess fluid are not properly excreted. Oliguria is often one of the earliest and most important warning signs of AKI, especially in hospitalized or critically ill patients.

Swelling in the legs, ankles, face, or around the eyes: When the kidneys cannot remove excess fluid from the body, fluid accumulates in tissues. This leads to visible swelling, particularly in dependent areas such as the legs and ankles, and sometimes around the eyes.

Shortness of breath (SOB): Fluid overload caused by kidney failure can result in fluid accumulation in the lungs (called pulmonary edema). This makes breathing difficult and may cause rapid or laboured breathing. Shortness of breath in AKI can indicate a serious complication requiring immediate medical attention.

Fatigue and weakness: As waste products such as urea and creatinine build up in the bloodstream, they affect overall body function. Additionally, electrolyte imbalances and anemia may also develop. These changes contribute to generalized weakness, low energy levels, and decreased physical stamina.

Nausea, vomiting, and loss of appetite: The buildup of toxins in the blood (uremia) irritates the gastrointestinal system. This can result in nausea, vomiting, metallic taste in the mouth, and loss of appetite. These symptoms are common when kidney dysfunction becomes more pronounced.

Chest pain or pressure: In severe acute kidney injury (AKI), excess fluid may build up around the heart (pericardial effusion), or electrolyte disturbances such as high potassium may affect heart rhythm. These changes can cause chest discomfort or pressure and may indicate a life-threatening complication.

High blood pressure: The kidneys play a key role in controlling blood pressure by managing fluid balance and hormone release. When kidney function declines, fluid retention and hormonal imbalance lead to higher blood pressure.

Confusion or mood changes: Accumulation of toxins and severe electrolyte imbalances can affect brain function. Patients may experience confusion, reduced alertness, irritability, or altered mental status. In advanced cases, this can progress to severe neurological complications.

Flank pain: Pain in the side of the lower back may occur when AKI is caused by obstruction (such as kidney stones) or inflammation. It can indicate increased pressure within the kidneys or associated infection.

A sudden decline in kidney function occurs due to decreased blood flow to the kidneys, direct kidney damage, or obstruction of urine flow. The acute kidney injury etiology is commonly classified into prerenal, intrinsic (intrarenal), and postrenal causes. These categories help identify the underlying factors contributing to kidney injury and guide appropriate management.

Prerenal cause of acute kidney injury

• Severe dehydration 
• Major blood loss or trauma
• Low blood pressure (shock)
• Sepsis (severe infection)
• Heart failure or cardiogenic shock
• Severe liver disease

Intrarenal cause of acute kidney injury

• Acute tubular necrosis 
• Certain medications 
• Autoimmune diseases 
• Vasculitis 

Postrenal cause of acute kidney injury

• Enlarged prostate
• Kidney stones
• Tumors compressing urinary tract
• Blood clots
• Ureteral strictures

Severe dehydration: A drop in blood volume reduces blood flow to the kidneys. Since the kidneys need adequate blood flow to filter waste products and balance electrolytes, decreased blood flow lowers the glomerular filtration rate (GFR). This leads to buildup of waste products like urea and creatinine. If prolonged, it can cause prerenal acute kidney injury.

Major blood loss or trauma: Significant hemorrhage reduces blood volume and oxygen delivery to the kidneys. The body prioritises blood flow to vital organs, further decreasing kidney perfusion and causing prerenal AKI.

Low blood pressure (shock): In shock states, systemic hypotension reduces the pressure required to push blood through the glomeruli. Without sufficient perfusion pressure, the kidneys cannot filter blood effectively. Prolonged hypotension may first cause prerenal AKI and, if uncorrected, can progress to intrinsic kidney damage.

Sepsis (severe infection): Sepsis causes widespread inflammation and vasodilation throughout the body, leading to decreased effective circulating blood volume and hypotension. Inflammatory mediators also increase vascular permeability, causing fluid to leak from blood vessels into tissues. These changes reduce blood flow to the kidneys. 

Heart failure or cardiogenic shock: When the heart cannot pump effectively, cardiac output decreases. As a result, less blood reaches the kidneys. Reduced renal perfusion lowers GFR and causes retention of nitrogenous waste, leading to prerenal AKI.

Severe liver disease: Advanced liver disease (such as cirrhosis) can cause abnormal blood circulation and reduced effective blood flow to the kidneys. A condition known as hepatorenal syndrome may develop, where kidney function declines despite structurally normal kidneys. 

Acute tubular necrosis (ATN): This happens when kidney tubular cells are destroyed as a result of chronic low blood flow or toxic exposure. The damaged tubules cannot filter waste correctly, resulting in abrupt kidney failure.

Certain medications: Some medicines can reduce blood flow to the kidneys or directly damage kidney tissues. Drugs such as certain antibiotics, pain relievers (NSAIDs), contrast dyes, and chemotherapy agents may trigger acute kidney injury, especially in high-risk patients.

Autoimmune diseases: In autoimmune conditions, the immune system attacks kidney tissues, causing inflammation of the filtering units. This damage reduces the kidneys’ ability to remove waste and regulate fluids, leading to acute kidney injury.

Vasculitis: Vasculitis causes inflammation and narrowing of blood vessels supplying the kidneys. Reduced blood flow can deprive kidney tissues of oxygen, resulting in sudden impairment of kidney function.

Enlarged prostate: An enlarged prostate can block the flow of urine from the bladder. When urine cannot drain properly, pressure builds up in the urinary tract and backs up toward the kidneys. This obstruction reduces kidney function and may lead to postrenal acute kidney injury (AKI) if not relieved promptly.

Kidney stones: Kidney stones can obstruct the ureters. A complete or severe blockage prevents urine from passing, causing increased pressure inside the kidneys.

Tumors compressing the urinary tract: Tumors in or near the urinary tract (such as bladder, prostate, or pelvic tumors) may compress or block urine flow. When urine drainage is obstructed, it leads to back pressure in the kidneys, reducing their ability to filter blood effectively.

Blood clots: Blood clots within the urinary tract can block urine flow. Similar to stones or tumors, this obstruction causes urine to accumulate and increases pressure inside the kidney.

Ureteral strictures: These are abnormal narrowing of the ureters, often due to prior surgery, infection, or injury. This narrowing restricts urine flow from the kidneys to the bladder. Continuous obstruction increases pressure within the kidney and can lead to acute kidney injury.

Certain patient characteristics, comorbid conditions, and clinical exposures increase the likelihood of developing AKI. Identifying these risk factors is essential for early recognition, prevention, and timely management to reduce morbidity and mortality. The frequent risk factors of acute kidney injury include:

Modifiable risk factors

Factors that can be changed or controlled to reduce the risk of a disease.

• Sepsis 
• Major surgery 
• ICU admission–related factors
• Use of nephrotoxic drugs
• Severe dehydration
• Exposure to contrast dye

Non-modifiable risk factors

Factors that cannot be changed and are inherent

• Advanced age
• Underlying chronic conditions (e.g., CKD, diabetes, hypertension)
• Patient with heart failure and liver disease

Sepsis: Sepsis is a severe, widespread infection that causes inflammation, low blood pressure, and impaired blood flow to vital organs. This lowers kidney perfusion and inflammatory damage make sepsis one of the leading risk factors for AKI.

Major surgery: During major surgeries, fluctuations in blood pressure, blood loss, use of anesthesia, and exposure to certain medications can temporarily reduce kidney blood flow. Cardiac surgeries, in particular, are strongly associated with postoperative AKI.

ICU admission–related factors: Patients admitted to the ICU are usually critically ill and may have unstable blood pressure, severe infections, or multi-organ failure. They often require strong medications and mechanical ventilation, all of which increase the likelihood of kidney injury.

Use of nephrotoxic drugs: Certain medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), some antibiotics, and other toxic agents, can directly injure kidney cells or reduce blood flow within the kidneys.

Severe dehydration: Loss of body fluids from vomiting, diarrhea, fever, or burns reduces circulating blood volume. When kidney blood flow decreases significantly, it can lead to prerenal AKI if not corrected promptly.

Exposure to contrast dye: Contrast agents used in imaging procedures (such as CT scans or angiography) may cause temporary kidney injury, especially in patients with diabetes, CKD, or dehydration. This condition is referred to as post contrast acute kidney injury.

Advanced age: With increasing age, kidney function naturally declines due to reduced kidney blood flow and loss of functioning kidney units (nephrons). Elderly patients also commonly have multiple medical conditions and take several medications, which increases their vulnerability to acute kidney injury during illness, surgery, or dehydration.

Underlying chronic conditions: If a person is suffering from chronic diseases like diabetes, hypertension, and chronic kidney disease (CKD) reduce the kidney’s functional reserve. When an additional stress, such as infection, low blood pressure, or medication exposure occurs, the kidneys may not tolerate it well, which increases the risk.

Patients with heart failure and liver disease: Heart failure reduces effective blood circulation to the kidneys, while severe liver disease alters blood flow and fluid balance. Both conditions affect kidney perfusion and make the kidneys more susceptible to acute damage.

Acute kidney injury is largely preventable if risk factors are identified early and appropriate precautions are taken. The main aim of prevention is to maintain adequate renal perfusion, avoid kidney toxins, and promptly manage underlying conditions. This includes:

• Maintaining proper hydration
• Managing chronic conditions
• Avoiding nephrotoxic substances
• Early management of infections & sepsis
• Avoiding contrast dyes
• Proper perioperative care
• Prevent postrenal obstruction

Maintaining proper hydration: It is essential to ensure adequate blood flow to the kidneys. Dehydration from vomiting, diarrhea, burns, or blood loss needs to be corrected promptly with oral or intravenous fluids, while avoiding fluid overload.

Managing chronic conditions: Conditions like diabetes, hypertension, chronic kidney disease (CKD), and heart failure all reduce vulnerability to AKI. Proper blood sugar and blood pressure control, as well as regular monitoring of renal function, all contribute to kidney health.

Avoiding nephrotoxic substances: Medications like NSAIDs, aminoglycosides, certain antifungals, chemotherapy drugs, and radiographic contrast agents are important. If these drugs are necessary, they need to be used in the lowest effective dose with dose adjustment according to renal function.

Early management of infections and sepsis: This helps to prevent kidney damage caused by hypotension and inflammation. Prompt antibiotic therapy, adequate fluid resuscitation, and maintenance of blood pressure are crucial.

Avoiding contrast dyes:  Avoiding unnecessary contrast dyes, especially in high-risk patients, reduces the risk of contrast-induced kidney injury. Adequate hydration before and after procedures further reduces the risk.

Proper perioperative care: This includes maintaining blood pressure and adequate fluid balance, which helps to prevent reduced kidney blood flow and ischemic injury.

Preventing postrenal obstruction: Early detection and treatment of urinary retention, prostate enlargement, or kidney stones also protects against AKI.

Acute kidney injury vs Chronic kidney disease

Both Acute kidney injury (AKI) and chronic kidney disease (CKD) affect how well the kidneys filter waste and balance fluids, but they differ mainly in how quickly they develop, how long they last, and whether they are reversible. The table below discusses about the differences between AKI and CKD: