Leukemoid Reaction: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Leukemoid Reaction?
A primary care doctor usually finds the problem first and starts the workup. Depending on the cause, they may refer you to a hematologist, a specialist in blood disorders, or an infectious disease specialist. A direct primary care or concierge doctor can often order the initial tests and manage simple causes directly.
What is a leukemoid reaction?
A leukemoid reaction is a condition in which the body makes far too many white blood cells, the cells that fight infection. The word means "like leukemia," because the blood counts can look similar to leukemia, a cancer of the blood. The key difference is that a leukemoid reaction is not cancer. It is the body's response to another problem, and counts usually return to normal once that problem is treated.
White blood cells are made in the bone marrow, the soft tissue inside your bones. Serious infection or certain drugs can prompt the marrow to release a very large number of these cells into the blood. The result can look alarming, but the cause is often treatable.
Symptoms
A leukemoid reaction itself often causes no symptoms. Most symptoms come from the condition that triggered it, such as fever, chills, night sweats, tiredness, or weight loss. Some people feel short of breath or notice fullness in the belly if the spleen becomes enlarged.
Causes and who gets it
Serious infections are the most common cause. Severe pneumonia, tuberculosis, and other widespread infections can push white blood cell counts very high. Certain cancers, some medicines, and some toxins can also trigger the reaction. People of any age can be affected.
How doctors diagnose it
Doctors usually start with a complete blood count. If the count is very high, the next step is often a blood smear, in which a specialist studies the cells under a microscope. Doctors may also test for the Philadelphia chromosome, a marker found in leukemia but not in a leukemoid reaction.
Treatment
There is no treatment aimed at the reaction itself. Instead, doctors treat the condition that caused it. If a bacterial infection is the trigger, antibiotics usually bring the count back down. If a medication is the cause, stopping or changing that drug often helps.
When to see a doctor
See a doctor for a fever that will not go away, unexplained weight loss, night sweats, or lasting tiredness. If a blood test has shown a very high white blood cell count, follow up promptly. Seek care quickly for trouble breathing, confusion, or a very high fever.
Common questions
Is a leukemoid reaction cancer?
No. It is not cancer, even though blood counts can look like leukemia. It is the body's response to an infection, medication, or other illness. Counts usually settle once the cause is treated.
How high does the white blood cell count go?
Counts often rise above 50,000 cells per microliter, which is far above the normal range. The exact number varies. Doctors look at the type and maturity of the cells as well as the count.
Can a leukemoid reaction come back?
It can happen again if the same kind of trigger returns, such as another severe infection. Treating the underlying cause each time is what brings counts back down.
How long does it take for counts to return to normal?
This varies from person to person. Many people see counts improve within days to weeks after the underlying cause is treated, but some causes take longer.
Sources
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
