Acute Kidney Injury
Acute kidney injury is a sudden loss of kidney function that can happen within hours or days. While this condition can be serious and even life-threatening without treatment, many people recover fully when the underlying cause is found and treated quickly.
Table of contents
- What is acute kidney injury?
- What causes acute kidney injury?
- Who is at risk?
- Signs and symptoms
- How is it diagnosed?
- Treatment and management
- Recovery and long-term outlook
What is acute kidney injury?
Acute kidney injury, or AKI, happens when your kidneys suddenly stop working properly[1]. This can range from minor loss of kidney function to complete kidney failure[2]. The condition used to be called acute renal failure[3].
Your kidneys are bean-shaped organs that filter waste products and extra fluid from your blood. When they suddenly can’t do this job, harmful levels of waste and chemicals can build up in your body[2]. The blood’s chemical makeup may get out of balance[2].
AKI normally happens as a complication of another serious illness. It’s not the result of a physical blow to the kidneys, as the name might suggest[4]. This type of kidney damage is usually seen in older people who are unwell with other conditions and the kidneys are also affected[4].
The condition is common, especially among hospitalized patients. AKI can be seen in up to 7% of hospital admissions and 30% of intensive care unit admissions[3]. It affects over 750,000 people in the United States each year and around 2 million people worldwide[6].
What causes acute kidney injury?
The causes of AKI can be divided into three main categories based on where the problem occurs[5].
Prerenal causes happen when there is reduced blood flow to the kidneys. Most cases of AKI are caused by reduced blood flow to the kidneys, usually in someone who’s already unwell with another health condition[4]. This reduced blood flow could be caused by low blood volume after bleeding, excessive vomiting or diarrhea, or severe dehydration. It can also result from the heart pumping out less blood than normal because of heart failure, liver failure, or sepsis (a severe infection that affects the whole body)[4]. Certain medicines that reduce blood pressure or blood flow to the kidneys can also cause this problem[4].
Intrinsic renal causes happen when there is damage within the kidney itself. AKI can be caused by a problem with the kidney itself, such as inflammation of the filters in the kidney (called glomerulonephritis), the blood vessels (vasculitis), or other structures in the kidney[4]. This may be caused by a reaction to some medicines, infections, or the liquid dye used in some types of X-rays[4]. Damage from some poisons, infections, and medicines such as ibuprofen can also harm the kidneys directly[7].
Postrenal causes happen when urine cannot drain properly from the kidneys. A sudden blockage that stops urine from flowing out of the kidneys can cause AKI[5]. This may be the result of a blockage affecting the drainage of the kidneys, such as an enlarged prostate, a tumor in the pelvis (such as an ovarian or bladder tumor), or kidney stones[4].
Who is at risk?
You’re more likely to get AKI if you fall into certain groups or have specific health conditions[4].
Age and existing health conditions increase your risk. You have a greater chance of getting acute kidney injury if you are an older adult (aged 65 or over), or if you already have a kidney problem such as chronic kidney disease[4]. Having a long-term disease such as heart failure, liver disease, or diabetes also increases your risk[4].
Certain medical situations put extra stress on your kidneys. You are more likely to have AKI if you are already very ill and in the hospital or intensive care unit. Heart or belly surgery or a bone marrow transplant can make you more likely to have kidney problems[7]. Being dehydrated or unable to maintain your fluid intake independently also increases risk[4]. Having a severe infection or sepsis is another important risk factor[4].
Medicines can affect kidney function. Taking certain medications increases your risk, including non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, or blood pressure medicines such as ACE inhibitors or diuretics[4]. Diuretics help the kidneys get rid of extra fluid from the body, but may become less helpful when a person is dehydrated or suffering from a severe illness[4]. Being given aminoglycosides, a type of antibiotic usually only given in hospital, is another risk factor[4].
Signs and symptoms
Many people experience few or no symptoms in the early stages of kidney injury. However, AKI may still cause damage even though you feel fine[6]. Some people may not have any symptoms and are diagnosed on the basis of a routine laboratory blood test[6].
When symptoms do appear, they can include several different problems. Symptoms of AKI may include feeling sick or being sick (nausea and vomiting), diarrhea, and dehydration[4]. You may notice that you are peeing less than usual[4]. Little or no urine when you try to urinate is a warning sign[7].
Other symptoms affect how you feel and think. Confusion or trouble concentrating can occur[2]. You may feel extremely tired (fatigue)[2], drowsy, anxious, or restless[7]. Poor appetite or food tasting metallic, along with headaches, can also happen[5].
Physical symptoms often involve swelling and discomfort. Swelling, particularly around your hands, ankles, or feet, can develop because of fluid buildup[2]. This fluid buildup can also cause shortness of breath[2]. You may have pain in the belly or in the side below the ribs[2]. Some people experience muscle cramps, dry or itchy skin, and changes in blood pressure[5].
How is it diagnosed?
A doctor may suspect AKI if you are in an “at risk” group and suddenly fall ill, or if you get symptoms of AKI[4].
The main test for diagnosing AKI is a blood test. AKI is usually diagnosed with a blood test to measure your levels of creatinine, a chemical waste product produced by the muscles[4]. If there’s a lot of creatinine in your blood, it means your kidneys are not working as well as they should[4]. A sample of your blood may show fast-rising levels of urea and creatinine, which helps show how your kidneys are working[9].
According to widely accepted guidelines, AKI is diagnosed when there is an increase in serum creatinine by 0.3 mg/dL or more within 48 hours, an increase in serum creatinine to 1.5 times or more than the baseline of the prior 7 days, or urine volume less than 0.5 mL per kilogram of body weight per hour for at least 6 hours[3].
Urine tests provide additional information. You may be asked to give a urine sample[4]. Measuring how much urine you pass in 24 hours may help find the cause of your kidney failure[9]. A sample of your urine may show something that suggests a condition that might explain kidney failure[9]. Urine can be tested for protein, blood cells, sugar, and waste products, which may give clues to the underlying cause[4].
Imaging tests help identify blockages and other problems. Imaging tests such as ultrasound and CT scans can show your kidneys[9]. An ultrasound scan should reveal if the cause is a blockage in the urinary system, such as an enlarged prostate or bladder tumor[4]. Ultrasonography of the kidneys should be performed in most patients, particularly in older men, to rule out obstruction[3].
Other investigations help understand the cause. Doctors need to know about any other symptoms, such as signs of sepsis or signs of heart failure, any other medical conditions, and any medicine that’s been taken in the past week, as some medicines can cause AKI[4]. In some cases, your healthcare professional may suggest removing a small sample of your kidney tissue for lab testing, called a biopsy[9].
Treatment and management
Treatment for acute kidney injury most often means a hospital stay. Most people with acute kidney injury are already in the hospital[9]. How long you’ll stay in the hospital depends on the reason for your acute kidney injury and how quickly your kidneys recover[9].
The first priority is treating the underlying cause. Treatment for acute kidney injury involves finding the illness or injury that damaged your kidneys[9]. Your doctor or a kidney specialist (nephrologist) will try to treat the problem that is causing your kidney injury[7]. Treatment can vary widely, depending on the cause. For example, your doctor may need to restore blood flow to the kidneys, stop any medicines that may be causing the problem, or remove or bypass a blockage in the urinary tract[7].
General supportive care helps your body cope while kidneys recover. Management includes treatment of the underlying cause and supportive care, such as renal replacement therapy[5]. You may need to increase your intake of water and other fluids if you’re dehydrated[4]. Adequate fluid balance should be maintained in patients with acute kidney injury by using isotonic solutions (such as normal saline)[3]. You may need antibiotics if you have an infection, or to stop taking certain medicines (at least until the problem is sorted)[4]. A urinary catheter, a thin tube used to drain the bladder, may be needed if there’s a blockage[4].
Preventing waste buildup and complications is essential. At the same time, the doctor will try to stop wastes from building up in your body and prevent other problems[7]. You may take medicines to get rid of extra fluid and keep your body’s minerals in balance[7]. Additional supportive care measures may include optimizing nutritional status and glycemic control[12].
Diet modifications support kidney recovery. You also may need to follow a special diet to keep your kidneys from working too hard[7]. Talk to your doctor or a dietitian about what type of diet may be best for you. You may need to limit sodium, potassium, and phosphorus[17].
Some patients need dialysis. You may have dialysis, a treatment that does the work of your kidneys until they recover[7]. It will help you feel better[7]. Renal replacement therapy (dialysis) is indicated for refractory hyperkalemia (dangerously high potassium levels), volume overload, intractable acidosis (severe acid-base imbalance), uremic encephalopathy (confusion from waste buildup), pericarditis or pleuritis (inflammation around the heart or lungs), and removal of certain toxins[3].
Recovery and long-term outlook
Many people make a full recovery from AKI. Most people with AKI make a full recovery[4]. Your chance of a full recovery depends on what caused the problem, how quickly the cause was treated, and what other medical problems you have[7]. Doctors sometimes can fix the problems that cause kidney injury. The treatment takes a few days or weeks. These people’s kidneys will work well enough for them to live normal lives[7].
Some people develop long-term kidney problems. However, other people may have permanent kidney damage that leads to chronic kidney disease[7]. People who have experienced AKI are at increased risk of developing chronic kidney disease in the future[5]. A small number of them will need to have regular dialysis or a kidney transplant[7].
The condition can be serious and life-threatening. AKI ranges from mild to severe. If severe, ongoing and not treated, it can be fatal[2]. Without quick treatment, abnormal levels of salts and chemicals can build up in the body, which affects the ability of other organs to work properly. If the kidneys shut down completely, this may require temporary support from a dialysis machine, or lead to death[4]. AKI is associated with a high rate of adverse outcomes; mortality rates range between 25 and 80 percent, depending on the cause and the clinical status of the patient[12].
Follow-up care is important. Follow-up care is a key part of your treatment and safety[17]. Be sure to make and go to all appointments. Long-term monitoring of kidney parameters after AKI is recommended[21]. Make sure that anyone treating you for any health problem knows that you have had AKI[17].
