Medical Oncologist
Blood tests and organ effects
Uric acid and tumour lysis syndrome
When some fast-growing cancers respond quickly to treatment, dying cancer cells release uric acid, potassium and phosphate into the blood faster than the kidneys can clear them. This is tumour lysis syndrome. It is rare, serious and mostly happens in the first days of treatment for blood cancers. Fluids, medicines and frequent blood tests prevent most cases.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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In the first days of treatment, get help immediately for any of these
Passing very little urine or none · vomiting that stops you keeping fluids down · a racing, pounding or irregular heartbeat · muscle cramps, twitching or spasms · severe weakness · confusion, unusual drowsiness or a seizure · swelling with breathlessness · fainting. Call your helpline or go to the nearest emergency department and say clearly that the person has just started treatment for cancer.
The short answer
What is tumour lysis syndrome?
Tumour lysis syndrome happens when a large number of cancer cells break down very quickly, usually because treatment is working fast. As the cells burst, they release their contents into the bloodstream: uric acid, potassium and phosphate. If these build up faster than the kidneys can clear them, uric acid and phosphate can form crystals in the kidneys, potassium can disturb the heart rhythm, and calcium can fall, causing cramps and spasms. Without prevention, it can lead to kidney failure, dangerous heart rhythms and seizures.
It is rare overall, but it is well recognised and mostly predictable. It happens most often in the first days of treatment for fast-growing blood cancers such as acute leukaemias and some aggressive lymphomas, especially when there is a large amount of cancer, a high white cell count, or existing kidney problems. It can occasionally happen with other fast-responding cancers and with some newer targeted medicines. Because doctors know who is at risk, most cases are prevented with fluids, medicines that lower uric acid, and frequent blood tests. This page explains the condition; it cannot interpret your results or tell you your personal risk.
Prevention starts before treatment
People at risk are usually given extra fluids and a uric acid-lowering medicine before the first dose.
Blood tests are frequent at first
Uric acid, potassium, phosphate, calcium and kidney function may be checked several times a day in high-risk cases.
It usually settles after the first days
The risk is highest early and falls as the cancer load reduces.
If you are starting treatment for a blood cancer, ask your team whether you are at risk of tumour lysis and what monitoring is planned.Not sure whether this applies to you?
Ask an oncologistWho is at risk
Factors that raise the risk of tumour lysis
- Fast-growing blood cancers
- Acute lymphoblastic and acute myeloid leukaemia, Burkitt lymphoma and other aggressive lymphomas carry the highest risk.
- A large amount of cancer
- Very enlarged glands, a large tumour mass or a very high white cell count increase the number of cells breaking down at once.
- Existing kidney problems
- Kidneys that already filter less well cannot clear the released substances as quickly.
- High uric acid before treatment
- Raised uric acid or potassium on baseline tests signals higher risk.
- Dehydration
- Low fluid levels reduce urine flow and make crystals more likely to form.
- Certain medicines
- Some very effective targeted medicines, such as venetoclax in chronic lymphocytic leukaemia, need careful step-by-step dose increases with monitoring.
How it is prevented
What your team does to prevent tumour lysis
Assess your risk
Your team looks at your cancer type, its size, your blood counts and your kidney and uric acid tests before starting.
Start extra fluids
Fluids by drip, and sometimes by mouth, keep urine flowing to flush released substances out.
Lower uric acid
Medicines such as allopurinol, or rasburicase for higher risk, stop uric acid building up or break it down.
Monitor closely
Blood tests, urine output, weight and sometimes heart rhythm are checked frequently in the first days.
Act quickly on changes
Abnormal salts are corrected, fluids adjusted, and in severe cases a kidney specialist may arrange dialysis for a short time.
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What this page cannot tell you
It cannot tell you your personal risk of tumour lysis or interpret your uric acid, potassium, phosphate or kidney results. These depend on your cancer, its size, your kidney function and your treatment, and your team assesses them.
It also cannot tell you whether you need to be admitted or how long monitoring will last. People at higher risk are often treated in hospital for the first days; lower-risk people may be monitored as outpatients.
Why hospital stays may be advised
Close monitoring several times a day is easier in hospital, and changes can be treated straight away.
Measuring urine output
You may be asked to pass urine into a container so staff can measure it. This is an important check on the kidneys.
Drinking as advised
If you are asked to drink extra fluids, keep a bottle nearby and sip steadily through the day and night.
Diet during the risk period
Your team may advise avoiding high-potassium foods or supplements for a short time. Follow their guidance.
Uric acid medicines
Allopurinol and rasburicase are given for a short time. Rasburicase is not suitable for people with G6PD deficiency, so tell your team if you know you have it.
Targeted tablets at home
Some medicines are started at low doses and increased weekly with blood tests. Keep every test appointment during this period.
Children are monitored carefully
Childhood leukaemias carry risk too, and paediatric teams follow similar prevention steps.
It does not mean treatment is failing
Tumour lysis is a sign that cancer cells are breaking down quickly. The aim is to manage it safely while treatment continues.
Family can help watch
Relatives can help track drinking and urine, and notice drowsiness, confusion or twitching early.
Weight checks show fluid balance
During the risk period you may be weighed once or twice a day. A rising weight with less urine can mean fluid is building up, which helps your team adjust drips or give medicines to increase urine flow before problems develop.
Telling staff how you feel matters
Nurses rely on you to report nausea, cramps, tingling, palpitations or feeling unusually sleepy. Speak up straight away, even at night, rather than waiting for the next round of checks.
Tell your team about gout or kidney stones
A history of gout, kidney stones or high uric acid may raise the risk and affects which medicines are chosen. Mention it before treatment starts.
What to do next
Ask whether you are at risk and what prevention and monitoring are planned, drink fluids as advised, keep urine and blood test checks, take uric acid medicines as prescribed, and seek emergency help for very little urine, palpitations, cramps, confusion or seizures.
Commonly believed
Four beliefs about tumour lysis syndrome
"Everyone on chemotherapy gets tumour lysis."
It is rare and mainly affects people with fast-growing blood cancers or a large amount of cancer at the start of treatment.
"It means the treatment is harming me."
It happens because treatment is breaking down cancer cells quickly. It is managed so treatment can continue safely.
"Extra fluids are just to keep me comfortable."
Fluids are a key part of prevention, flushing out uric acid and salts to protect the kidneys.
"Once I go home, the risk is over."
The risk falls after the first days, but some tablet treatments need monitoring for weeks. Keep all tests.
Questions we are asked
Common questions about tumour lysis syndrome
What is tumour lysis syndrome?
A condition where cancer cells break down so quickly that uric acid, potassium and phosphate build up in the blood, which can harm the kidneys and heart rhythm.
Who is at risk?
Mainly people starting treatment for fast-growing blood cancers, those with a large amount of cancer, high white cell counts or kidney problems.
What are the signs?
Passing little urine, nausea and vomiting, cramps or twitching, palpitations, weakness, confusion or seizures, usually in the first days of treatment.
How is it prevented?
With extra fluids, medicines that lower uric acid, and frequent blood and urine checks in the first days.
Why is uric acid checked?
Uric acid released from cancer cells can form crystals in the kidneys. Checking it guides prevention.
Will I need to stay in hospital?
People at higher risk often do for the first days. Your team will decide based on your risk.
Is it dangerous?
It can be serious if not prevented or treated, but with monitoring most cases are avoided or managed early.
Does it mean my treatment is working?
It shows cancer cells are breaking down quickly. Your team manages it so treatment can continue safely.
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Sources
- Cancer.Net (ASCO) — Tumor Lysis Syndrome
- Cancer Research UK — Blood tests
- Macmillan Cancer Support — Blood tests
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.
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