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Leukaemoid reaction or leukaemia: telling a very high count apart | CION Cancer Clinics
A leukaemoid reaction is a very high white cell count caused by the body fighting something else, such as a severe infection, heavy bleeding or a medicine. Leukaemia is a cancer of the bone marrow. The two can look alike on one report. The difference is that a reaction has a cause and settles when it is treated. This page explains how doctors tell them apart. At CION Cancer Clinics, our haematologist reviews abnormal blood reports with you, orders only the tests that answer your question and explains each result plainly.
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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 a leukaemoid reaction, and how is it different from leukaemia?
- How do doctors tell a leukaemoid reaction from leukaemia?
- What can cause a leukaemoid reaction?
- What tests will be done to find out which it is?
- What do families often misunderstand about a very high count?
- What should you do with a report like this?
- Common questions about leukaemoid reaction and leukaemia
The short answer
What is a leukaemoid reaction, and how is it different from leukaemia?
A leukaemoid reaction is a very high white cell count caused by the body fighting something else, such as a severe infection or major stress. Leukaemia is a cancer of the bone marrow, and the high count comes from the marrow itself.
Why the two get confused
On a routine blood report, both can show a white cell count many times above the usual range. Both can show young white cells that are not normally seen in the blood. That is why the name exists: "leukaemoid" means "looks like leukaemia". Looking alike on one report is not the same as being the same illness.
The key difference
A leukaemoid reaction has an outside cause. When that cause is treated, the count comes down. Leukaemia does not settle on its own, because the problem is in the marrow, the spongy tissue inside your bones where blood cells are made.
Reading your own number
Reference ranges for white cells differ between laboratories, so read your result against the range printed on your report. A single high result is always read alongside how the person is, what illness they have, and repeat tests.
This page explains the difference. It cannot tell you which one is behind your own report.
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When a very high count cannot wait
If the person with a very high white cell count is confused, very breathless, drowsy, has a high fever with shivering, is bleeding, or has sudden weakness on one side, go to the nearest emergency department now or call 108. Take the blood report with you. Do not wait for a routine appointment to discuss it.
Side by side
How do doctors tell a leukaemoid reaction from leukaemia?
Leukaemoid reaction
Leukaemia
A clear cause, such as a severe infection or bleeding
No outside cause explains the count
The count falls once the cause is treated
The count stays high or keeps rising
Mostly mature white cells, with few very young ones
Often many blast cells, very immature cells, on the blood film
Haemoglobin and platelets often normal or mildly changed
Haemoglobin and platelets are often low
Gene tests on blood are normal
Gene tests may find a change, such as BCR-ABL in CML
Not sure whether this applies to you?
Ask an oncologistWhat sets it off
What can cause a leukaemoid reaction?
Usually the person is already unwell with something serious, and the high count is part of the body's response to it.
Severe infection
Blood infections, pneumonia, tuberculosis, typhoid, a severe gut infection with loose motions, and abscesses can push the count very high. In children, whooping cough is a known cause.
Heavy bleeding or red cell breakdown
After a large bleed, or when red cells are destroyed quickly, the marrow works flat out and releases white cells along with red ones.
Medicines
Steroids and growth factor injections given to raise white cells can both cause a large rise. Never stop a prescribed medicine because of a report. Ask the doctor who prescribed it.
Major body stress
Serious burns, a large operation, severe pancreatitis or poisoning can all raise the count sharply.
A cancer elsewhere
Some solid tumours, such as certain lung or kidney cancers, release signals that drive the marrow to make more white cells.
This is not leukaemia, but it still needs a proper search for the cause.The work-up
What tests will be done to find out which it is?
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A full history and examination
The doctor looks for infection, recent surgery, bleeding and new medicines, and checks for a large spleen or swollen glands.
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A repeat count and a blood film
A specialist looks at the blood cells under a microscope. The mix of mature and young cells often points one way or the other.
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Treating the cause and rechecking
If an infection is found, it is treated and the count is repeated. A count that falls with recovery strongly supports a reaction.
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Gene tests on blood
If doubt remains, blood can be tested for changes linked to leukaemia, such as BCR-ABL. A normal result makes some leukaemias very unlikely.
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A bone marrow test, if needed
When the blood tests cannot settle it, a haematologist may advise a marrow sample. Ask where it will be done and when results are expected.
Commonly believed
What do families often misunderstand about a very high count?
"A count this high must be leukaemia."
A very high count in someone who is seriously ill with an infection is often a reaction. The height of the number alone does not decide it. The cause, the blood film and the repeat count do.
"The report said leukaemoid, so it is a mild leukaemia."
Leukaemoid is not a type of leukaemia. It means the blood looks similar at first glance. It is a reaction to something else, and the name describes the look, not a cancer.
"Once the fever is gone, we do not need to recheck."
The repeat count is what confirms the reaction has settled. Skipping it leaves the question open. Go back for the test your doctor asks for, even if the person feels well.
"A bone marrow test is dangerous, so we will avoid it."
A marrow test is a routine procedure done under local anaesthetic, which numbs the area. Many people do not need one. When a haematologist advises it, avoiding it can delay a clear answer.
Being straight with you
What should you do with a report like this?
Show the report to the doctor treating the illness, the same day if the person is unwell. If there is no clear cause, or the count stays high after recovery, ask to see a haematologist, a doctor who specialises in blood.
What to bring
Bring every blood report you have, in date order, with the list of medicines the person takes. Include any growth factor injections or steroids. A trend over several reports tells the doctor far more than one alarming number.
What this page cannot tell you
It cannot tell you which of the two you are facing. It also cannot tell you how serious the underlying illness is. Only a doctor who has examined the person and seen the full reports can judge that. If leukaemia is found, the outlook depends on the type and many personal factors, and your haematologist is the right person to explain it.
How CION can help
CION's haematology team, led by Dr. Basudev Pokhrel, reviews the reports, presents complex cases at a tumour board, and helps you reach the right tests at qualified centres where they are done.
Questions we are asked
Common questions about leukaemoid reaction and leukaemia
Can a leukaemoid reaction turn into leukaemia?
No. A leukaemoid reaction is the body's response to another illness, and it does not change into a cancer. The count settles once that illness is treated. If the count does not settle, the doctor looks again for a cause, which may include testing for a marrow condition that was there from the start.
How long does it take for the count to come down?
It depends on the cause and how quickly it responds to treatment. With an infection that clears well, the count usually falls steadily as the person recovers. Your doctor will tell you when to repeat the test. A count that is not falling as expected is a reason to see a haematologist.
My father has TB and a very high count. Is it cancer?
Tuberculosis is a known cause of a leukaemoid reaction, so the count may well be a response to the infection. The doctors will usually watch the count as TB treatment continues. Tell them if he has swollen glands, a swollen tummy, bruising or bleeding, because those need looking at more closely.
Can a child have a leukaemoid reaction?
Yes. Children can react strongly to infections such as whooping cough or a severe chest infection. Newborns can also show high counts for other reasons. A paediatrician will look at the whole child, not just the number, and will involve a paediatric haematologist if the picture is unclear.
Is chronic myeloid leukaemia the one it is confused with?
Often, yes. Chronic myeloid leukaemia, or CML, can also show a very high count of mostly mature white cells. A blood test for the BCR-ABL gene change usually separates the two. A normal result points away from CML, and a haematologist interprets it with the rest of the picture.
Should the steroids or growth factor injection be stopped?
Do not stop or change any prescribed medicine on your own. These medicines can raise the white count, and the treating doctor knows that. Show them the report and ask whether the rise fits what they expected. They will decide whether anything needs changing.
Does a normal blood film rule out leukaemia?
A film showing mostly mature cells and no blasts is reassuring, but it does not rule everything out on its own. Some conditions need gene tests or a marrow test to confirm or exclude them. Your haematologist decides which further tests, if any, are worth doing.
Is testing covered by Aarogyasri or insurance?
Tests done as part of an admission or an approved treatment plan are often covered by Aarogyasri, CGHS, ECHS, EHS, PM-JAY or cashless insurance. Some gene tests may not be. Scheme rules change, so check your current cover with the helpline or your insurer before the tests are booked.
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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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Sources
- NHS — Chronic myeloid leukaemia
- Cancer Research UK — Chronic myeloid leukaemia (CML)
- Leukaemia & Lymphoma Society — Chronic myeloid leukemia
- American Society of Hematology — Blood basics
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
Related pages
Raised Counts and Reactive ChangesEvery kind of raised blood count explained in one placeWhen a High Count Needs Marrow TestingWhen a marrow test is advised, and whyReactive Thrombocytosis After Infection or SurgeryThe same kind of reaction in plateletsLeukaemia guideIf a haematologist has found leukaemia
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Holding a report with a very high count?
Share it with us. CION's haematology team will look at the whole picture and tell you what the next step should be. One helpline serves every CION centre.