What Happens When My Neutrophils Are Low? An Expert Guide to Neutropenia

September 26, 2025 •

4 min read

Approximately one in three people receiving chemotherapy will experience neutropenia, a condition defined by low neutrophil counts. Knowing what happens when my neutrophils are low is crucial for protecting your health, as a reduced number of these vital white blood cells weakens the body's primary defense against infection.

Quick Summary

When your neutrophil count is low, a condition known as neutropenia, your body's ability to fight off bacterial and fungal infections is severely compromised, increasing your overall vulnerability to illness. The severity of the risk is directly linked to how low your count is, and symptoms often appear only after an infection has already begun to develop.

Key Points

Immune System Risk: Low neutrophils weaken the immune system, dramatically increasing your risk of bacterial and fungal infections.
Hidden Symptoms: Neutropenia often has no specific symptoms; instead, the signs you experience are from the infections you acquire.
Immediate Action for Fever: A fever is a medical emergency for someone with neutropenia and requires prompt medical attention to prevent serious complications like sepsis.
Multiple Causes: Causes range from cancer treatments and autoimmune diseases to viral infections and genetic conditions, with treatment dependent on the root cause.
Regular Monitoring: Diagnosis is typically made via a Complete Blood Count (CBC) with differential, and the Absolute Neutrophil Count (ANC) is used to monitor severity.
Proactive Prevention: Taking simple precautions like meticulous hand washing and avoiding sick people can significantly reduce infection risk while your counts are low.

Understanding Neutrophils and Neutropenia

Neutrophils are the most abundant type of white blood cell, acting as the first line of defense in the immune system. Produced in the bone marrow, they patrol the body and are among the first responders to infection, engulfing and destroying harmful pathogens like bacteria and fungi. A low count of these essential immune cells, a condition called neutropenia, weakens the immune response and leaves the body more susceptible to infections.

Neutropenia is a common condition that can range in severity from mild to life-threatening. The risk of serious infection increases as the neutrophil count decreases. It is typically diagnosed through a standard complete blood count (CBC) test, which measures the absolute neutrophil count (ANC).

The Causes of Low Neutrophils

Neutropenia can be caused by a wide range of factors that either suppress the production of neutrophils in the bone marrow or increase their destruction in the bloodstream. The underlying cause is key to determining the appropriate treatment.

Medications and Treatments

Chemotherapy and Radiation: Many cancer treatments target rapidly dividing cells, including cancer cells and healthy cells in the bone marrow that produce neutrophils. This is one of the most common causes of neutropenia.
Other Drugs: Certain medications, including some antibiotics, anti-seizure drugs, and antipsychotic medications, can also suppress neutrophil production.

Infections

Viral Infections: Viruses such as HIV, hepatitis B and C, Epstein-Barr virus (mononucleosis), and measles can all trigger neutropenia.
Bacterial Infections: Severe bacterial infections like sepsis can lead to increased consumption of neutrophils, causing their levels to drop.

Autoimmune Disorders

Lupus and Rheumatoid Arthritis: In autoimmune diseases, the immune system mistakenly attacks the body's own cells. In some cases, it produces antibodies that destroy neutrophils.

Bone Marrow Disorders and Cancers

Leukemia and Lymphoma: Cancers that affect the bone marrow can displace the normal blood-producing cells, leading to lower neutrophil counts.
Aplastic Anemia and Myelodysplastic Syndromes: These bone marrow diseases result in the underproduction of all blood cell types.

Genetic and Nutritional Factors

Congenital Neutropenia: Some rare genetic disorders, like Kostmann's syndrome, are present from birth and cause severely low neutrophil counts.
Benign Ethnic Neutropenia: Certain ethnic groups, particularly people of African, Middle Eastern, and West Indian descent, can have naturally lower neutrophil counts without an increased risk of infection.
Nutrient Deficiencies: A deficiency in vitamin B12 or folate can impair bone marrow function and lead to neutropenia.

Common Signs and Symptoms

Neutropenia itself does not always cause symptoms, especially in mild cases. The most significant signs are typically those of a resulting infection, which can be more severe or unusual than in people with normal neutrophil counts.

Symptoms of infection with neutropenia:

Fever (over 100.4°F or 38°C) is a critical sign, known as febrile neutropenia, and requires immediate medical attention.
Chills and sweats.
Persistent cough or sore throat.
Mouth sores or swelling and redness of the gums.
Pain or burning during urination.
Diarrhea.
Unusual skin rashes, redness, or swelling.
Fatigue or feeling generally unwell.

How Is Neutropenia Diagnosed and Treated?

Diagnosis

Complete Blood Count (CBC): A routine CBC test is the first step. The absolute neutrophil count (ANC) is calculated from the results. An ANC below 1,500/µL is the threshold for a neutropenia diagnosis.
Medical History and Physical Exam: Doctors will review your symptoms, medication history, and any recent infections to identify potential causes.
Further Testing: If the cause is not obvious, additional tests may be necessary. This can include a bone marrow biopsy, imaging scans, or testing for vitamin deficiencies or autoimmune markers.

Treatment

Treatment is highly dependent on the cause and severity of the condition.

Managing Infections: Antibiotics are often prescribed at the first sign of infection, especially with fever, to prevent potentially life-threatening complications like sepsis.
Medication Adjustments: If the cause is a drug, stopping or changing the medication may be the solution.
Growth Factors: Medications called granulocyte colony-stimulating factors (G-CSFs) can be injected to stimulate the bone marrow to produce more neutrophils.
Treating the Underlying Cause: In cases caused by an underlying condition like an autoimmune disease or cancer, treating the primary illness is the long-term solution.
Bone Marrow Transplant: For severe congenital neutropenia or bone marrow failure, a stem cell transplant may be required.

Important Precautions and Comparison of Neutropenia Types

If you have been diagnosed with neutropenia, it is essential to take precautions to minimize the risk of infection. These include frequent hand washing, avoiding large crowds or sick individuals, and taking extra care with food safety and minor injuries. The Centers for Disease Control and Prevention (CDC) provides detailed guidance on preventing infections during neutropenia.


Type of Neutropenia	Cause	Key Features
Acute	Viral infections, chemotherapy	Short-term; neutrophil counts often recover once the cause is resolved.
Chronic	Bone marrow disorders, autoimmune issues	Long-term condition requiring ongoing management and monitoring.
Cyclic	Rare genetic mutation (ELANE gene)	Neutrophil counts rise and fall in a predictable cycle (approx. every 3 weeks).
Autoimmune	Immune system attacking neutrophils	Can occur with conditions like lupus or rheumatoid arthritis.
Benign Ethnic	Genetic variant (Duffy phenotype)	Found in certain ethnic groups; not associated with an increased infection risk.

Conclusion

Low neutrophils, or neutropenia, is a serious condition that can leave the body vulnerable to infections. While many causes exist, ranging from temporary viral infections to chronic bone marrow disorders, early diagnosis and management are crucial. If you have been diagnosed with neutropenia or are undergoing a treatment that can cause it, proactive measures like good hygiene and prompt medical attention for any signs of infection are your best defense. Regular monitoring and communication with your healthcare provider are vital for staying healthy and preventing complications.

Frequently Asked Questions

Neutropenia is generally diagnosed when the absolute neutrophil count (ANC) falls below 1,500 cells per microliter. The severity is categorized further, with mild neutropenia (1,000-1,500), moderate (500-1,000), and severe (below 500), which carries the highest risk of serious infection.

A fever is a serious warning sign and requires immediate medical evaluation. You should contact your healthcare provider or go to the emergency room immediately, especially if you are on chemotherapy, as this could be a sign of a life-threatening infection.

No, not always. The seriousness depends on the cause and degree of the reduction. Mild neutropenia may not cause any issues and could resolve on its own. In other cases, such as in benign ethnic neutropenia, the count is naturally lower without an increased risk of infection.

While a balanced diet is important for overall immune health, it cannot typically cure neutropenia on its own, especially when caused by chemotherapy or other serious medical conditions. Certain nutritional deficiencies, like B12 or folate, can cause neutropenia and may be treated with supplements, but this is best managed under medical supervision.

Preventing infection is crucial. Frequent hand washing, avoiding large crowds and sick people, practicing proper food safety, and maintaining good personal hygiene are key. Your doctor may also recommend specific vaccinations or prophylactic antibiotics.

Growth factor injections, such as G-CSF (Filgrastim), stimulate the bone marrow to increase its production of neutrophils. They are often used to help boost low counts, particularly following chemotherapy, to reduce the duration of neutropenia and lower the risk of infection.

Acute neutropenia is temporary, often caused by an infection or short-term medication, and resolves once the trigger is gone. Chronic neutropenia is a persistent condition that requires long-term management and is typically caused by more serious underlying issues like autoimmune diseases or bone marrow disorders.