Acute kidney injury (AKI) is sudden damage to the kidneys that causes them to not work properly. It can range from minor loss of kidney function to complete kidney failure.
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.
This type of kidney damage is usually seen in older people who are unwell with other conditions and the kidneys are also affected. Read more about who's at risk of AKI.
It's essential that AKI is detected early and treated promptly. The role of the kidneys is to:
- filter – removing waste and water from the blood (as urine, via the bladder)
- clean the blood
- keep the bones healthy
- look after blood pressure
- stimulate the bone marrow to make blood
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.
Symptoms of acute kidney injury
In the early stages of AKI, there may not be any symptoms. The only possible warning sign may be that the person isn't producing much urine, although this isn't always the case.
However, someone with AKI can deteriorate quickly and suddenly experience any of the following:
- nausea and vomiting
- high blood pressure
- abdominal pain
- slight backache
- a build-up of fluid in the body (oedema)
Even if it doesn't progress to complete kidney failure, AKI needs to be taken seriously. It has an effect on the whole body, changes how some drugs are handled by the body and could make some existing illnesses more serious.
AKI is different to chronic kidney disease, where the kidneys gradually lose function over a long period of time.
Who's at risk of acute kidney injury?
You're more likely to get AKI if:
- you're aged 65 or over
- you already have a kidney problem, such as chronic kidney disease
- you have a long-term disease, such as heart failure, liver disease or diabetes
- you're dehydrated or unable to maintain your fluid intake independently
- you have a blockage in your urinary tract (or are at risk of this)
- you have a severe infection or sepsis
- you're taking certain medicines, including non-steroidal anti-inflammatory drugs (NSAIDS, such as ibuprofen) or blood pressure drugs, such as ACE inhibitors or diuretics; diuretics are usually beneficial to the kidneys, but may become less helpful when a person is dehydrated or suffering from a severe illness
- you're given aminoglycosides – a type of antibiotic; again, this is only an issue if the person is dehydrated or ill, and these are usually only given in a hospital setting
AKI is estimated to affect 13-18% of people admitted to hospital. It can affect both adults and children.
Causes of acute kidney injury
Most cases of AKI are caused by reduced blood flow to the kidneys, usually in someone who is already unwell with another health condition.
This reduced blood flow could be caused by:
- low blood volume after bleeding, excessive vomiting or diarrhoea, or as seen with severe dehydration
- the heart pumping out less blood than normal as a result of heart failure, liver failure or sepsis, for example
- problems with the blood vessels – such as inflammation and blockage in the blood vessels within the kidneys (a rare condition called vasculitis)
- certain medicines (see above), which can affect the blood supply to the kidney – other medicines may cause unusual reactions in the kidney itself
AKI can also be caused by a problem with the kidney itself, such as glomerulonephritis. This may be caused by a reaction to some drugs, infections or contrast medium (the liquid dye used in some types of X-rays).
It may also be due to a blockage affecting the drainage of the kidneys, such as:
When should AKI be suspected?
A doctor may suspect AKI in people known to be at risk who suddenly fall ill or develop symptoms which suggest complications of AKI.
AKI may also be suspected in people who have been unwell for a while and have either:
- chronic kidney disease
- a urinary system disease
- new or worsening urinary symptoms
- symptoms or signs of a disease affecting the kidneys and other organs
Diagnosing acute kidney injury
AKI can be diagnosed after measuring urine output and doing blood tests.
Blood levels of creatinine – a chemical waste product produced by the muscles – will be measured. Healthy kidneys filter creatinine and other waste products from the blood and these are excreted, in the form of urine. It's an easy and quick marker of kidney function, with higher levels of creatinine in the blood indicating poorer kidney function.
In adults, a diagnosis of AKI can be made if:
- blood creatinine level has risen from the baseline value for that person (by 26 micromoles per litre or more within 48 hours)
- blood creatinine level has risen over time (by 50% or more within the past 7 days)
- they are passing much less urine (less than 0.5ml per kg per hour for more than 6 hours)
In children and teenagers, doctors should use the plasma creatinine level to calculate the estimated glomerular filtration rate (estimated glomerular filtration rate (eGFR). A diagnosis of AKI is made if they have a 25% or greater fall in eGFR within the past 7 days.
Read more about AKI in children.
Investigating the underlying cause
Urine can be tested for protein, blood cells, sugar and waste products, which may give clues to the underlying cause.
Doctors also need to know about:
An ultrasound scan should reveal if the cause is a blockage in the urinary system, such as an enlarged prostate or bladder tumour.
Treating acute kidney injury
Treatment of AKI depends on the underlying cause and extent of illness. In most cases, treating the underlying problem will cure the AKI.
GPs may be able to manage mild cases in people who aren't already in hospital. They may:
- advise stopping any medication that may be causing the situation, or making it worse – it may be safe to resume some of these when the problem is sorted
- treat any underlying infections
- advise on fluid intake to prevent dehydration (which could cause or worsen AKI)
- take blood tests to monitor levels of creatinine and salt – to check how well a person is recovering
- refer to a urologist (genitourinary surgeon) or nephrologist (kidney specialist) if the cause isn't clear or if a more serious cause is suspected
Admission to hospital is necessary in cases where:
- there's an underlying cause that needs urgent treatment – such as a urinary blockage, or if the person is seriously unwell; most people need hospital care to treat the underlying cause, allowing the AKI to get better
- there's a risk of urinary blockage – because of prostate disease, for example
- the person's condition has deteriorated, and regular blood and urine tests are needed to monitor how well their kidneys are working
- the person has a complication of AKI
The majority of people who recover from AKI end up with a very similar level of kidney function as they had before they became ill, or go on to have normal kidney function.
However, some people go on to develop chronic kidney disease or long-term kidney failure as a result. In severe cases, dialysis – where a machine filters the blood to rid the body of harmful waste, extra salt and water – may be needed.
Preventing acute kidney injury
Those at risk of AKI should be monitored with regular blood tests if they become unwell or start new medication. It's also useful to check how much urine you're passing.
Any warning signs of AKI, such as vomiting or producing little urine, require immediate investigation for AKI and treatment. People who are dehydrated, or at risk of dehydration, may need to be given fluids via a drip.
Any medicine that seems to be making the problem worse, or directly damaging the kidneys needs to be stopped, at least temporarily.
The National Institute for Health and Care Excellence (NICE) has produced detailed guidelines on preventing, detecting and managing AKI.
Read the NICE guidelines here.
Complications of acute kidney injury
The most serious complications of acute kidney injury are:
- high levels of potassium in the blood – in severe cases, this can lead to muscle weakness, paralysis and heart rhythm problems
- fluid in the lungs (pulmonary oedema)
- acidic blood (metabolic acidosis) – which can cause nausea, vomiting, drowsiness and breathlessness