What is acute kidney injury (AKI)?

Acute kidney injury (AKI) is a sudden and recent reduction in the level of kidney function.  This is detected by a blood test but can also be detected if someone is passing less urine than normal.

AKI is often caused by problems elsewhere in the body, but can be caused by diseases starting in the kidney in some cases.

Most cases of AKI get better with the correct treatment but sometimes AKI can be more serious and need more specialist assessment and treatment in hospital.

What does AKI mean?

Acute

The term ‘acute’ means an illness that has developed recently. This can be within the last 6 weeks, but often AKI develops over a period of days. ‘Acute’ does not always mean that a problem is severe, just that it developed recently. 

Kidney

Your kidneys are like filters, and they remove waste products from your blood. A blood test can measure these waste products, and this is how AKI is identified. Sometimes kidneys cannot get rid of excess water. This can make your legs swell or make it harder to breathe. AKI usually affects both kidneys in the same way. 

Injury

Injury means that  the kidneys have lost some of their function or are impaired, usually by another illness or sometimes by medication. 

How is AKI detected?

Doctors rely on blood tests to confirm that someone has AKI, specifically

 a waste product in the blood called creatinine. If the level of this waste product has increased, the kidneys are not working as well as normal. Severity of AKI is linked to how much creatinine is in the blood. The more creatinine, the more severe the aKI . It is important to identify the cause of AKI and treat this quickly. .

Other factors, such as the amount of urine you pass, will help the doctor assess how severe the AKI is and what treatment is required.

AKI may have no other symptoms other than the symptoms of the illness leading to it.

If it is severe, it may cause symptoms such as sickness and generally feeling unwell, and the amount of urine you pass may be reduced. 

What causes AKI?

There are many causes of AKI. One of the first steps doctors will take if someone has AKI is to try and find the cause or causes. Often there is more than one factor leading to AKI. 

Some of the important causes of AKI are:

• Infection – any severe infection can ‘stress’ the kidneys, even if the infection is not in the kidneys themselves 
• Dehydration – severe dehydration will reduce the blood flow to the kidneys.  Without blood flow providing oxygen to the kidneys, the kidneys do not work as well. 
• Drugs – sometimes drugs can cause AKI. This does not necessarily mean they were prescribed incorrectly, but for anyone with AKI it is important for the doctors to know what medication you are taking. This includes drugs not on prescription, especially painkillers. 
• Blockages to the flow of urine – urine is made in the kidneys and must pass down long thin tubes to the bladder. The bladder releases the urine from time to time. Blockages to the drainage tubes or the bladder can cause AKI. A simple scan can usually detect blockages. 
• Surgery – an operation can cause AKI, especially if there is infection and/or dehydration. During surgery the blood flow to the kidneys may be reduced and this can lead to AKI.  Before having an operation, the anaesthetic team will review your medication and may make some changes to try and protect your kidneys. 
• Chronic kidney disease – if your kidneys are not working perfectly in the first place and you get ill for any reason, you are more likely to get AKI than someone with perfectly normal kidneys. (link to CKD) 
• Kidney diseases – there are several kidney diseases that can develop rapidly and cause AKI (link to vasculitis and myeloma)

What tests will I need?

• Blood tests - Anyone with AKI requires blood tests to look for the causes of AKI and monitor progress. You may not need to go to hospital if the cause is clear and you get better when it is treated.  If you do not get better or it is severe, you may need to go to hospital for further tests and even be admitted to hospital for treatment. 
• Urine test - Urine is tested for infection and to see if blood and protein is leaking from the kidneys. 
• Ultrasound scan - If you are in hospital, a scan of the kidneys may be performed. This will show if there is blockage to the flow of urine from the kidneys or bladder. An ultrasound will not show everything, for example if there is infection in the kidneys the scan may look normal. 
• CT scan – sometimes more detailed scans, may be required. A CT scan is where you lie on a couch and are moved through a large circular scanner.
• Specific kidney blood tests -  You may need blood tests to look for kidney diseases which can cause AKI.
• Biopsy -  If doctors think there is a disease inside the tissue of the kidney causing AKI, then it may be necessary to perform a kidney biopsy to confirm the diagnosis. A biopsy is when a small piece of kidney is removed with a needle and then examined under the microscope. 

What treatment will I need?

This depends on what caused the AKI, and how severe it is. 

If you have dehydration or an infection, both common causes of AKI, you may be given fluids or antibiotics through a needle in your arm . 

It is usually important to monitor the amount of urine you are passing. Athin tube called a catheter may be placed into your bladder, so the urine can drain into a bag to be measured. . 

In more serious cases of AKI, if waste products build up in your blood or there is too much fluid in your body, you may need dialysis..

Dialysis is a treatment that does the job of your kidneys. Usually, blood is cleaned through a machine. Sometimes fluid can be passed in and out of the tummy. (link to section on dialysis). 

If the illness causing AKI affects other parts of the body, or causes very low blood pressure or your breathing is affected, you may need care in a Critical Care Unit (or Intensive Care Unit). Tubes may be put into blood vessels to monitor the blood pressure more closely, and to give drugs to increase the blood pressure. If breathing is very difficult it may be necessary to have a machine help with breathing (an artificial ventilator). In addition, you may receive dialysis during this time.

How long will I be in hospital?

In some cases, AKI may resolve in a couple of days with fluid and antibiotics. In other cases, the illness affecting the kidneys and the rest of the body may be so severe that recovery takes weeks or months. . 

Will I make a full recovery from AKI?

This varies from person to person and depends on what caused the AKI, how severe it was, and what other health problems you have. 

Most of the time, kidneys recover completely back to normal. But sometimes, if the kidneys were not normal to start with, the AKI was severe, or you have other health conditions,  kidneys may not make a complete recovery. When there is a permanent loss of kidney function this is called chronic kidney disease (CKD) and is a long-term condition.

Sometimes people may need ongoing dialysis treatment.. 

If the AKI caused you to be in the hospital, you may feel weak and it may take time to get your full strength back.

If you had difficulty walking before an episode of AKI,  your recovery or rehabilitation could take weeks. Specialist rehabilitation services may be required, and some people need help at home from carers. 

What can be done to stop me from getting AKI again?

When you have had an AKI, ask your doctor to tell you what warning signs to watch for in the future. This can help prevent it happening again. . For example, you may been told to see a doctor sooner if you feel unwell; after 1 day rather than waiting 3 or 4 days.

A doctor can also advise which medicines to avoid especially if you are dehydrated ( for example if you have diarrhoea and vomiting, or you are in a hot place or country).

If your AKI was caused by an infection, it is important to check the infection has fully cleared after you have finished your antibiotics . For example, if your AKI was due to a urine infection, your doctor may suggest a urine test about a month after your recovery to check the infection has gone.

Last reviewed May 2026
Next review May 2029

Reviewed by Kathryn Johnson  
Lead Advanced Clinical Practitioner
& Charlotte Templeton Advanced Clinical Practitioner
Acute Kidney Injury Team
University Hospital Southampton NHS Foundation Trust

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The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.