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Tumour lysis syndrome: recognising it early | CION Cancer Clinics
Tumour lysis syndrome is an emergency when, soon after treatment starts, a person passes little urine, has cramps, an irregular heartbeat, confusion or a fit. Go to the nearest emergency department or call 108. It happens when many cancer cells break down at once and overload the kidneys with salts and waste. This page covers the signs, who is at risk and how teams try to prevent it. At CION Cancer Clinics, our haematology team supports patients and families through treatment, cost questions and life at home.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- What is tumour lysis syndrome, and when is it an emergency?
- Which symptoms could be tumour lysis syndrome?
- Who is more likely to get tumour lysis syndrome?
- How does the team try to prevent it?
- What do families often misunderstand about tumour lysis syndrome?
- What can this page not tell you?
- Common questions about tumour lysis syndrome
The short answer
What is tumour lysis syndrome, and when is it an emergency?
Tumour lysis syndrome happens when a large number of cancer cells break down at once and flood the blood with salts and waste. It is an emergency when urine drops sharply, the heartbeat feels irregular, muscles cramp or twitch, or the person becomes confused or has a fit. Then go to the nearest emergency department now or call 108.
Why treatment itself can trigger it
Chemotherapy and some newer blood cancer medicines kill cancer cells quickly. When those cells burst, they release potassium, phosphate and uric acid into the blood. The kidneys have to clear all of it. If there is too much at once, the kidneys struggle, and the salt levels in the blood go badly out of balance. High potassium can upset the heart rhythm. Low calcium can cause cramps and fits.
When it usually appears
It most often starts in the first few days after treatment begins. Sometimes it starts before any treatment, in a very fast-growing cancer that is breaking down on its own. That is why the team checks blood tests so often at the start of treatment, sometimes more than once a day.
Many of the early changes show up only on blood tests, before you feel anything. Keep every blood test the team books, even if the person feels fine.
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Go to emergency now if
Someone who has recently started treatment for leukaemia, lymphoma or another fast-growing cancer is passing very little or no urine, has a racing or irregular heartbeat, fainting, muscle cramps or twitching, confusion, or a fit. Call 108 or go to the nearest emergency department. Tell them what treatment was started and when, and take the latest blood reports. Do not wait to see whether it settles overnight.
Not sure whether this applies to you?
Ask an oncologistWhat you may notice
Which symptoms could be tumour lysis syndrome?
What you may notice
What may be behind it
Passing much less urine, dark urine or swollen ankles
The kidneys are struggling to clear waste and fluid
A fluttering, racing or skipping heartbeat, or fainting
High potassium affecting the heart rhythm
Cramps, twitching, tingling round the mouth or fingers
Calcium falling as phosphate rises
Feeling sick, vomiting, loose motions, loss of appetite
Salt changes and kidney strain, or simply treatment side effects
Confusion, unusual tiredness or a fit
Severe salt imbalance or kidney failure
Pain in the side or lower back
Uric acid crystals collecting in the kidneys
Who is at risk
Who is more likely to get tumour lysis syndrome?
The risk comes from how much cancer there is, how fast it grows, how well the kidneys work and how strong the treatment is. Your team weighs all four before treatment starts.
Fast-growing blood cancers
Acute leukaemias and some aggressive lymphomas carry the highest risk, because the cells divide and break down quickly.
Higher risk with
- A very high white cell count
- Burkitt lymphoma
- Acute lymphoblastic leukaemia
A large amount of cancer
Big lymph node masses, an enlarged spleen or liver, or cancer in the bone marrow mean more cells can break down at once.
Kidneys already under strain
Existing kidney disease, dehydration, low blood pressure or a high uric acid level before treatment all make it harder to clear the waste. Diabetes and high blood pressure can also play a part.
Strong or targeted treatment
Intensive chemotherapy and some targeted medicines used in chronic lymphocytic leukaemia work fast enough to cause it. Your team starts these with extra checks.
It is uncommon in slow-growing cancers, but not impossible.Leave a number, we will call you
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Before and after the first dose
How does the team try to prevent it?
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A risk check before treatment
Blood tests for kidney function, potassium, phosphate, calcium and uric acid, and a look at how much disease there is.
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Plenty of fluid
Many people are given fluid through a drip, starting before the first dose. You may be asked to drink more, and to keep a record of what goes in and what comes out.
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Medicines to lower uric acid
Your team may prescribe a medicine to keep uric acid down. Take it exactly as the team says. Do not stop it or change it yourself.
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Frequent blood tests in the first days
For higher-risk treatment, tests may be done several times a day, and some people stay in hospital for the start of treatment.
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Treatment if levels move
If salts rise or the kidneys slow, the team treats it quickly. A small number of people need kidney dialysis for a short time while the kidneys recover.
Commonly believed
What do families often misunderstand about tumour lysis syndrome?
"It means the treatment has failed."
It means cancer cells are breaking down quickly, which is what the treatment is meant to do. The danger is the waste they leave behind. It says nothing on its own about how well the cancer will respond in the long run.
"Vomiting after chemotherapy is normal, so we will wait."
Some sickness is common. But vomiting with very little urine, cramps or an odd heartbeat in the first days of treatment is a reason to go to emergency the same day. Dehydration also makes the kidneys struggle more.
"Drinking lots of water at home is enough."
Fluid helps, and your team may ask you to drink more. But it cannot replace the blood tests. Salt levels can go wrong while the person still feels well. If you have a kidney or heart condition, ask how much to drink, because too much can also cause harm.
"Once the first week is over, the risk is gone."
The risk is highest at the start, but it can return when a new, stronger treatment begins. Ask the team before each new treatment whether extra checks are planned.
Being straight with you
What can this page not tell you?
This page cannot tell you your own risk. That depends on the exact type of cancer, your blood results, your kidneys and the treatment chosen. Only the treating haematologist can put those together.
Blood results need context
A report showing a raised potassium, phosphate or uric acid, or a low calcium, does not by itself mean tumour lysis syndrome. Reference ranges differ between laboratories. A sample that sat too long before testing can show a falsely high potassium. Doctors read a single result alongside symptoms, the timing of treatment and repeat tests.
What to ask your team before treatment starts
Ask whether the planned treatment carries a risk of tumour lysis syndrome, how often blood tests will be done, whether the first doses will be given in hospital, and which number to call at night. If you live far from the treating centre, ask which nearby hospital to go to in an emergency, and keep a copy of the latest reports on your phone.
Questions we are asked
Common questions about tumour lysis syndrome
How soon after chemotherapy can tumour lysis syndrome start?
It most often starts within the first few days of treatment, and occasionally within hours of the first dose in very fast-growing cancers. It can also appear before treatment in some leukaemias and lymphomas. This is why blood tests are done so often at the start. Follow the testing schedule your team gives you.
Can it happen at home after discharge?
Yes, particularly with treatment given as tablets at home or when someone goes home soon after a first dose. Watch how much urine is being passed, and look out for cramps, a racing heartbeat, confusion or heavy vomiting. If any appear, go to the nearest emergency department or call 108.
Is tumour lysis syndrome the same as kidney failure?
Not exactly. Tumour lysis syndrome is the flood of salts and waste from breaking cancer cells. Kidney injury is one of the things it can cause. Many people have changes in blood salts without lasting kidney damage, especially when it is caught early and treated quickly.
Will the person need dialysis?
Most people do not. Fluids, medicines and close blood tests are usually enough. Dialysis, where a machine cleans the blood, is used when the kidneys cannot keep up or potassium stays dangerously high. When it is needed, it is often short term while the kidneys recover.
Should we stop the cancer treatment if we notice symptoms?
Do not stop or skip any medicine on your own. Go to emergency, say which treatment was started and when, and let the doctors speak to the treating haematologist. The team decides whether to pause, change or continue treatment once the blood results are back.
Can children get tumour lysis syndrome?
Yes. Children with acute lymphoblastic leukaemia or fast-growing lymphomas are among the higher-risk groups. A child may not say they feel unwell. Watch for fewer wet nappies or trips to the toilet, unusual sleepiness, twitching or fits, and go to emergency the same hour.
Does it only happen with blood cancers?
It is much more common in blood cancers, because they tend to grow fast and respond quickly to treatment. It is seen far less often in solid tumours, usually when the cancer is large and very sensitive to treatment. Ask your own oncologist whether it applies to you.
What should I carry when going to a local hospital?
Carry the latest blood reports, the discharge summary, a list of every medicine with the date treatment started, and the treating haematologist's name and number. A local doctor who does not know the patient can act far faster with these in hand. Keep photos of them on your phone as well.
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Addressed by landmark, because that is how this city navigates. A haematology consultation can be booked at any of these centres through one helpline, and your team will tell you where each test or treatment takes place.
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Sources
- National Cancer Institute — Definition of tumor lysis syndrome
- Cancer.Net — Managing physical side effects
- Macmillan Cancer Support — Cancer information and support
- Leukemia & Lymphoma Society — Leukemia
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
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Talk to us
Starting treatment and unsure about the risks?
If there are symptoms, go to emergency first. Otherwise, call the helpline and we will help you reach a haematologist who can review your reports. One helpline serves every CION centre.