Contrast Associated Acute Kidney Injury

Overview

Contrast-associated acute kidney injury (CA-AKI) means the kidneys suddenly become stressed and stop filtering as well as usual, shortly after you have a scan or procedure that uses a special dye called contrast. Contrast is a liquid that helps doctors see inside your body more clearly on X-rays, CT scans and some other tests. Your kidneys filter it out of your blood and pass it in your urine. In some people this extra work causes a short-term drop in kidney function. 'Acute kidney injury' simply means a sudden change over hours or days, not a long-term problem. Most people who get it recover fully.

It is not common in people with healthy kidneys. Most people who have a contrast scan do not develop it. It is more likely in people who already have reduced kidney function, are older, or are unwell and dehydrated at the time of the scan.

It can affect anyone who has contrast dye, but it is more likely in older adults, people with existing kidney problems, people with diabetes, heart failure or liver disease, people who are dehydrated or very unwell, and people who take certain medicines that are hard on the kidneys.

Symptoms

Common symptoms

• Often no symptoms at all — it is usually picked up on a blood test
• Passing less urine than usual
• Feeling more tired or weak than expected
• Feeling sick, or going off food
• Puffiness in the legs, ankles or face
• Mild breathlessness
• Feeling thirsty or light-headed

Symptoms in children

• Noticeably fewer wet nappies or trips to the toilet than usual
• Being sleepier or more irritable than usual
• Puffiness around the eyes, hands or feet
• Poor feeding or drinking
• Being sick or complaining of tummy ache
• Looking pale or more unwell than expected after a scan

Symptoms in older adults

• New confusion, drowsiness or being 'not themselves' — this can be the first sign in older people
• Passing much less urine, or needing to get up in the night less often
• Feeling very tired, weak or unsteady on the feet
• Poor appetite, weight loss or feeling sick
• Swelling in the legs or breathlessness when walking
• Becoming dehydrated quickly because of illness, heat or not drinking enough

Causes

Main causes

• Contrast dye used in scans and procedures — it can reduce blood flow to the kidneys and put short-term stress on kidney cells, especially when the kidneys are already working less well
• Being dehydrated or unwell around the time of the scan
• Having several tests with contrast close together
• A large amount of contrast being used, or contrast given directly into a vein in a fast dose
• Other stresses on the kidneys at the same time, such as low blood pressure, infection or some medicines

Risk factors

• Existing kidney disease, or a low kidney function reading on a blood test
• Being over 65
• Diabetes
• Heart failure, liver disease or other long-term illness
• Being dehydrated, or being very unwell at the time of the scan
• Taking certain medicines that affect the kidneys, such as some blood pressure medicines, some pain relievers, some diabetes medicines and some antibiotics
• Having a lot of contrast used, or having contrast scans repeatedly in a short time
• Being underweight or very frail
• Having had kidney problems after contrast before

When to see a doctor

See a doctor urgently if:

• You are passing much less urine than usual
• You cannot keep fluids down
• You feel very dizzy, faint or breathless
• You notice new swelling in your legs, ankles or face
• You feel much more unwell, unusually sleepy or confused

Book a routine appointment if:

• You are due a follow-up blood test and want to know when it should happen
• You are going to have another scan with contrast and want your kidney function checked first
• You are worried about your medicines and whether they are safe for your kidneys
• You feel more tired or less hungry than usual after a contrast scan

Diagnosis

Doctors find this by comparing blood tests of your kidney function before and after your scan. The main measure is creatinine, a waste product your kidneys normally remove. If creatinine rises in the days after contrast was given, and other causes have been ruled out, it is called contrast-associated acute kidney injury. Most cases are found this way rather than because you felt unwell.

Tests that may be done

• Blood tests to measure creatinine and your estimated glomerular filtration rate (eGFR) — a way of describing how well your kidneys are filtering
• A blood test before your scan to know your starting kidney function if you are at higher risk
• Urine tests to check for infection or protein in the urine
• Blood tests for salts and minerals such as potassium and sodium, which the kidneys help to balance
• An ultrasound scan of the kidneys in some cases, to check for other causes such as a blockage
• A review of your medicines, recent scans and how much fluid you have been drinking
• A check of your weight, blood pressure and fluid balance if you are in hospital

What to expect at your appointment

You will usually have a blood test before the scan if you are at risk, then another one within a few days afterwards. The follow-up test is quick and is often done at your GP surgery, a hospital clinic or a local health centre. If the results show a change, your doctor will repeat the tests until things settle and will review any medicines that might be putting strain on your kidneys. Most people have one or two extra blood tests and then no further treatment.

Treatment

There is no single medicine that reverses this problem. Treatment is about giving your kidneys the best chance to recover: keeping you well hydrated, reviewing medicines that could be adding strain, checking your blood tests, and treating anything else that is going on, such as infection or low blood pressure. In most cases the kidneys recover on their own over days to weeks.

Self-care at home

• Drink normally and do not restrict fluids unless a healthcare professional has told you to
• Attend any follow-up blood tests — they are the main way to know your kidneys have recovered
• Tell your pharmacist before buying any painkillers or cold remedies, as some can be hard on the kidneys
• Do not start or stop any prescription medicine without checking with your doctor first
• Avoid becoming dehydrated — drink regularly in hot weather and during illnesses that cause vomiting or diarrhoea
• Tell every healthcare professional you see that you had a kidney reaction to contrast, and when
• Rest when you need to, and return to normal activity gradually
• Note down any new symptoms such as swelling, less urine or breathlessness and report them

Medical treatments

Treatment is supportive. In hospital, fluids may be given through a drip to keep your kidneys well supplied with blood. Your care team will review your medicines and may pause one that could be adding strain — never stop a medicine yourself, as this decision depends on your full picture. Your urine output, weight, blood pressure and blood tests will be checked. Any other problem, such as an infection or low blood pressure, will be treated. Very occasionally, if kidney function drops a lot, short-term dialysis (a machine that filters the blood) may be needed while the kidneys recover. Dialysis is uncommon and is usually temporary.

When is surgery considered?

Surgery is not a treatment for this condition. Occasionally, if a scan or procedure with contrast is absolutely necessary and you are at high risk, your team may plan extra precautions such as more hydration, careful timing or a different type of imaging. Rarely, an ultrasound scan might show a blockage in the kidney that needs a procedure to relieve it — this is a different cause of kidney problems, not contrast injury.

Living with this condition

For most people this is a short episode, not a long-term condition. You may have a few extra blood tests over the following weeks. Once your kidney function is back to normal, life can carry on as usual. The main lasting thing to remember is that you had a reaction to contrast — write it down, tell your GP, and mention it before any future scan or procedure that might use dye.

Lifestyle tips

• Keep well hydrated, especially in hot weather, during exercise or when you are unwell
• Take medicines exactly as prescribed, and check with your pharmacist before using over-the-counter remedies
• Keep up with your regular check-ups for any long-term condition such as diabetes or high blood pressure
• Limit alcohol, which dehydrates the body and strains the kidneys
• Do not smoke — smoking harms blood vessels, including those in the kidneys
• Keep a simple note of your scan dates and any kidney reactions, so you can tell new doctors

Diet and exercise

There is usually no special diet for this short-term problem. Eat a balanced diet with plenty of vegetables, fruit, whole grains and protein, and drink enough fluid that your urine is pale yellow. If you have long-term kidney disease, diabetes or heart failure, your team may already have given you specific advice about salt, potassium or fluid — follow that advice rather than general rules. Gentle regular activity, such as walking, swimming or cycling, helps your heart and blood vessels and therefore your kidneys. Build back up gradually if you have been unwell, and ask your doctor before starting strenuous exercise soon after a hospital stay.

Mental health and emotional wellbeing

Being told something has gone wrong with your kidneys can be frightening, even when the problem is temporary. It is very common to feel anxious, especially before follow-up blood tests or before another scan. You might worry about future scans or feel uncertain about your health. These feelings usually ease once your results come back normal. If worry is affecting your sleep, appetite or mood, or lasting more than a few weeks, please talk to your GP or another healthcare professional — support is available and you do not have to manage alone.

Prevention

The risk can be greatly reduced, though not always removed completely. The most important step is knowing your kidney function before a contrast scan, so your team can plan around it. If you are at higher risk, your doctor may use a smaller amount of contrast, choose a different type of scan that does not need contrast, make sure you are well hydrated, and review medicines that could add strain. Always tell staff about any previous kidney problem after contrast, and about your other health conditions and medicines.

Vaccines

There is no vaccine for this condition. Keeping up to date with routine vaccinations, and with any vaccines your doctor recommends because of a long-term condition, helps you avoid infections that can be an extra strain on the kidneys.

Screening programmes

There is no general screening programme. Instead, a blood test of your kidney function is offered before a contrast scan when you are in a higher-risk group, and a follow-up blood test is arranged afterwards if needed. Ask about this if you are unsure whether a check is planned.

Complications

If left untreated

• Kidney function may stay reduced for longer than expected, and in a small number of people the change can be lasting
• Dangerous changes in salt and mineral levels in the blood, which can cause weakness, cramps or an irregular heartbeat
• Too much fluid building up, leading to swelling and breathlessness
• A longer hospital stay or a delay in other treatment you need
• A higher chance of future kidney problems, so monitoring and prevention matter at future scans
• Very rarely, temporary dialysis may be needed while the kidneys recover

Long-term outlook

The outlook is good for most people. In the majority of cases kidney function returns to its previous level within days to a few weeks, and many people have no lasting effects at all. Having this problem once does make it more important to protect your kidneys in future, so tell any healthcare professional before another contrast scan and keep up with routine checks for conditions such as diabetes and high blood pressure. With those simple steps, most people go on to live completely normal lives.

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