Neutrophils are the most abundant type of white blood cell and play a central role in protecting your body against bacterial and fungal infections.
If you recently had a Complete Blood Count (CBC) and noticed your neutrophil level is high or low, you may be wondering whether this is serious.
In many cases, mild changes in neutrophil levels are temporary and related to infection, stress, or medication use. However, significant or persistent abnormalities can sometimes indicate immune dysfunction or bone marrow disorders.
This guide explains:
- What neutrophils do
- What a normal absolute neutrophil count (ANC) looks like
- What causes high neutrophils (neutrophilia)
- What causes low neutrophils (neutropenia)
- When medical follow-up is necessary
Understanding your lab results in context is essential before drawing conclusions.
What are neutrophils?
Neutrophils are a type of granulocyte produced in the bone marrow. They represent approximately 50–70% of circulating white blood cells, making them the most numerous immune cell in the bloodstream.
They are part of the innate immune system, meaning they act as a rapid first line of defense against infections.
Neutrophils:
- Circulate in the bloodstream
- Migrate quickly to sites of infection or injury
- Engulf and destroy bacteria and fungi through phagocytosis
- Release antimicrobial enzymes and reactive oxygen species
Under a microscope, mature neutrophils are characterized by a multi-lobed nucleus and granular cytoplasm.
Because they respond rapidly to infection, neutrophil levels often increase during acute bacterial illnesses.
What is the function of neutrophils?
The main function of neutrophils is to fight specifically against bacteria by phagocytosis and bactericidal action, thanks to their ability to migrate through the tissues to the site of infection.
What is absolute neutrophil count (anc)?
The Absolute Neutrophil Count (ANC) measures the total number of neutrophils in a microliter of blood.
Doctors rely on the ANC rather than percentage because percentage values can be misleading if other white blood cell types are abnormal.
ANC is calculated as:
Total white blood cell count × percentage of neutrophils (including bands)
It is typically reported in:
cells per microliter (cells/µL)
or
×10⁹/L
ANC is the most clinically important measurement when assessing infection risk.
Neutrophils normal range
Neutrophils are the most numerous of all white blood cells: they represent the majority of circulating white blood cells (50 to 75%).
In most laboratories, a normal ANC is:
1,500 to 7,000 cells/µL
(1.5–7.0 × 10⁹/L)
Values may vary slightly depending on:
- Laboratory standards
- Age
- Ethnicity (benign ethnic neutropenia exists in some populations)
- Pregnancy
A single mildly abnormal value does not necessarily indicate disease.
Neutrophils count is usually determined by a complete blood count (CBC). The “normal value” is considered to be between 1,800 and 7,000 neutrophils per cubic millimeter (mm3) of blood.
That said, a count slightly below or above these values rarely reflects a problem.
In fact, we only start talking about neutropenia (abnormally low amount of neutrophils) when their level is less than 1700/mm3.
We also talk about neutrophilia when their rate is really higher than the average: above 8 000/mm3.
How Doctors Classify Neutropenia (Low Neutrophils)
Neutropenia is classified by severity because infection risk depends on how low the ANC is.
| ANC Level | Classification | Infection Risk |
|---|---|---|
| 1,000–1,500 | Mild neutropenia | Minimal |
| 500–1,000 | Moderate neutropenia | Moderate |
| < 500 | Severe neutropenia | High risk |
Severe neutropenia (ANC < 500) significantly increases the risk of serious bacterial infections and requires urgent medical evaluation.
This classification is widely used in clinical practice and oncology.
What does high neutrophils mean?
High neutrophils also called neutrophilia is not necessarily due to a disease.
We usually talk about neutrophilia when the rate is above 8 000/mm3.
It is especially common in people who smoke heavily. In addition, certain medications such as corticosteroids can also cause neutrophilia.
Apart from this, there are many other causes of neutrophilia, of varying severity. These include bacterial or parasitic infections, bleeding, inflammatory diseases (e.g. rheumatoid arthritis, “gout”), myocardial infarction and sometimes even cancer.
Neutrophilia is typically defined as:
ANC > 7,500–8,000 cells/µL
In most cases, neutrophilia is reactive and temporary.
Common causes include:
- Acute bacterial infections
- Physical stress (surgery, trauma)
- Smoking
- Corticosteroid use
- Inflammation (e.g., rheumatoid arthritis)
- Tissue injury (e.g., myocardial infarction)
Less commonly, persistent neutrophilia may be associated with:
- Chronic inflammatory disorders
- Certain bone marrow conditions
- Rare hematologic malignancies
Importantly, most cases of elevated neutrophils are caused by infection or inflammation rather than cancer.
What does low neutrophils mean? (neutropenia)
Low neutrophil count also called neutropenia can indicate many things, including anemia due to iron, vitamin B12 or folic acid deficiency.
Various parasitic or viral infections can also be the cause.
Apart from that, there is also the possibility of drug or alcohol intoxication, hyperthyroidism, acute leukemia or medullar aplasia (a disease in which the bone marrow does not produce enough blood cells, including white blood cells).
Neutropenia refers to:
ANC below 1,500 cells/µL
It can result from:
Decreased production (bone marrow suppression)
- Chemotherapy
- Aplastic anemia
- Vitamin B12 deficiency
- Folate deficiency
Increased destruction
- Autoimmune conditions
- Severe infections
Medication effects
- Certain antibiotics
- Antithyroid drugs
- Immunosuppressive therapies
Mild neutropenia without symptoms is often monitored with repeat testing.
Moderate to severe neutropenia requires medical evaluation due to infection risk.
Neutrophil Maturation and Development
Neutrophils develop through a carefully orchestrated process called granulopoiesis in the bone marrow. Beginning as myeloblasts, these precursor cells undergo several maturation stages—promyelocyte, myelocyte, metamyelocyte, band neutrophil—before becoming fully functional segmented neutrophils.
This development process takes approximately 7-10 days and is regulated by growth factors like granulocyte colony-stimulating factor (G-CSF). During maturation, neutrophils develop their distinctive multi-lobed nucleus and acquire specialized granules containing antimicrobial proteins, proteolytic enzymes, and oxidative compounds. These granules are classified as primary (azurophilic), secondary (specific), and tertiary (gelatinase) based on their contents and when they form during cell development. Under normal conditions, the bone marrow maintains a reserve pool of neutrophils that can be rapidly mobilized during infection or inflammation, allowing for the quick deployment of these critical immune cells when needed.
How Doctors Interpret Abnormal Neutrophil Counts
When evaluating abnormal neutrophil levels, clinicians follow a structured approach:
Step 1: Confirm the ANC
Ensure the value is accurate and review previous CBC results.
Step 2: Assess Symptoms
Fever, recurrent infections, mouth ulcers, or skin infections raise concern.
Step 3: Review Other Blood Values
- Are red blood cells low?
- Are platelets low?
- Is there lymphocytosis?
Multiple abnormal cell lines may suggest bone marrow involvement.
Step 4: Consider Recent Events
Recent infection, stress, surgery, or medication changes often explain temporary fluctuations.
Step 5: Determine Duration
Transient changes are common. Persistent abnormalities may require further evaluation such as peripheral smear or bone marrow testing.
Lab values are never interpreted in isolation.
When Should You See a Doctor?
Seek urgent medical care if low neutrophils are associated with:
- Fever (especially ≥100.4°F / 38°C)
- Chills
- Mouth sores
- Persistent infections
- Severe fatigue
In individuals undergoing chemotherapy, fever with neutropenia is considered a medical emergency.
Educational notice: This content is provided for informational and educational purposes only and is not intended as medical advice. Always consult a qualified healthcare professional for medical concerns.
