Yes, frequent infections can be a sign of leukemia. Leukemia fills the bone marrow with abnormal white blood cells that do not fight germs properly, and it crowds out the healthy neutrophils and other immune cells that normally do. The result is infections that come back often, last longer than expected, or do not respond well to treatment. Recurrent infections alone rarely mean leukemia, but together with fatigue, easy bruising or unexplained fever they deserve a blood test.
In my practice, questions about hematological disorders often begin with a patient who “keeps catching everything.” This article explains why leukemia weakens the immune system, which infection patterns should raise concern, and how infections are prevented and treated during leukemia care.
Why Leukemia Causes Frequent Infections
Leukemia is a cancer of the blood-forming cells. It begins in the bone marrow, where an abnormal clone of cells multiplies out of control. These abnormal white blood cells may be present in huge numbers, yet they cannot do the work of normal ones.
Several mechanisms combine to raise infection risk:
- Neutropenia – leukemia cells crowd out the precursors of neutrophils, the white cells that fight bacteria and fungi. A low neutrophil count is the single biggest driver of serious infection.
- Faulty immune cells – in chronic lymphocytic leukemia (CLL), the malignant B cells do not make useful antibodies, leading to low immunoglobulin levels (hypogammaglobulinemia).
- Treatment effects – chemotherapy, steroids and some targeted drugs further suppress the immune system.
- Broken barriers – mouth ulcers, gut inflammation and central lines give germs an easy way into the bloodstream.
Infection Risk by Neutrophil Count
The absolute neutrophil count (ANC) is the number I watch most closely. A normal adult ANC is roughly 1,500 to 8,000 cells per microliter.
| ANC (cells per microliter) | Category | Infection risk |
|---|---|---|
| 1,500 or more | Normal | Usual risk |
| 1,000–1,499 | Mild neutropenia | Slightly increased |
| 500–999 | Moderate neutropenia | Moderately increased |
| Below 500 | Severe neutropenia | High; fever is treated as an emergency |
Infection Patterns That Suggest Leukemia
Everyone gets colds. What makes me think about a blood problem is a pattern that does not fit ordinary illness. Warning signs include:
- Infections that return within weeks or keep coming back despite antibiotics.
- Unusual infections, such as oral thrush in an otherwise healthy adult, or fungal chest infections.
- Persistent fevers or night sweats without a clear source.
- Painful mouth ulcers, gum infections or slow-healing skin infections.
- Repeated pneumonia or sinus infections.
Other Symptoms That Often Appear Alongside
Leukemia rarely affects only the white cells. Because the marrow also makes red cells and platelets, infections often come with fatigue and pallor from anemia, easy bruising or nosebleeds from low platelets, unexplained weight loss, bone pain, and swollen lymph nodes, liver or spleen.
Leukemia can occur at any age. It is the most common cancer in children, where acute lymphoblastic leukemia predominates, while most adult cases, including CLL and acute myeloid leukemia, occur in older adults.
Causes and Risk Factors
The exact cause of leukemia is usually unknown. It results from acquired genetic changes in blood-forming cells. Recognized risk factors include previous chemotherapy or radiation therapy, genetic conditions such as Down syndrome, high-level benzene exposure, smoking (for acute myeloid leukemia), and some pre-existing marrow disorders.
These risk factors do not cause infections themselves. They simply make leukemia more likely, which is why a history that includes them lowers my threshold for testing someone with recurrent infections.
How Doctors Investigate Recurrent Infections
Diagnosing leukemia starts with a complete blood count (CBC) with differential and a blood smear. These show the number of white cells, red cells and platelets, and whether abnormal cells such as blasts are circulating. Leukemia can produce a very high, normal or low white count, so the smear and differential matter as much as the total.
| Test | What it shows |
|---|---|
| CBC with differential | Total white count, neutrophils, lymphocytes, hemoglobin, platelets |
| Peripheral blood smear | Blasts or other abnormal cells |
| Bone marrow biopsy | Confirms the diagnosis and type of leukemia |
| Flow cytometry and genetics | Subtype, risk group and treatment targets |
| Immunoglobulin levels | Antibody deficiency, especially in CLL |
| Cultures and imaging | The source and organism of a current infection |
A careful differential diagnosis matters because many other conditions cause frequent infections, including diabetes, HIV, inherited immune deficiencies, medicines and other hematological abnormalities.
Treating Leukemia and Preventing Infections
Treatment for leukemia may include chemotherapy, targeted therapy, immunotherapy and stem cell transplantation. Controlling the leukemia is the best long-term way to restore immunity, but infection protection runs alongside it:
- Prophylactic medicines – antibiotics, antivirals or antifungals during high-risk periods.
- Immunoglobulin replacement – for patients with low antibody levels and repeated serious infections, particularly in CLL.
- Growth factors – drugs such as G-CSF that help neutrophils recover faster after some treatments.
- Vaccination – inactivated vaccines such as influenza and pneumococcal vaccines are generally recommended; live vaccines are usually avoided.
- Everyday hygiene – handwashing, food safety, good mouth care and avoiding sick contacts.
Complications of Untreated Infections
In a person with leukemia, an infection can progress quickly to sepsis, a life-threatening reaction to infection. Serious infections may also force delays or dose reductions in leukemia treatment, which is why early action is so important.
When to See a Doctor
See a doctor for a blood test if you have infections that keep returning, especially with tiredness, bruising, weight loss or night sweats. If you are already being treated for leukemia, a temperature of 38°C (100.4°F) or higher, shaking chills, or feeling suddenly unwell needs urgent same-day care. Febrile neutropenia is a medical emergency, and antibiotics are ideally started within an hour.
Frequently Asked Questions
Can frequent colds be the only sign of leukemia?
It is uncommon. Most people with repeated colds have ordinary viral infections, especially parents of young children. Leukemia usually shows other signs too, such as fatigue, bruising or an abnormal blood count, so a simple CBC is often enough to reassure.
Why do people with a high white count still get infections?
In leukemia, the high count is made up mostly of abnormal cells that do not fight infection. Meanwhile, normal neutrophils and antibody-producing cells may be very low. The total number hides the real problem, which is why the differential count matters.
Which leukemia is most linked to repeated infections?
All types can cause them. Acute leukemias often cause severe neutropenia and sudden serious infections. Chronic lymphocytic leukemia commonly causes low antibody levels, leading to repeated chest and sinus infections over months or years.
Can I get vaccines if I have leukemia?
Most inactivated vaccines are safe and recommended, although the response may be weaker. Live vaccines are generally avoided during active treatment. Your hematology team will advise on timing around chemotherapy or transplant.
