Neutrophils are a type of white blood cell and key first responders of the immune system, forming the majority of circulating granulocytes and playing a central role in defending against bacterial and fungal infections. They are produced in the bone marrow, have a short lifespan in the circulation, and migrate rapidly to sites of infection or inflammation where they kill pathogens through phagocytosis, degranulation, and the formation of neutrophil extracellular traps (NETs).
Key points
- Normal range and variability: Neutrophil counts can vary by age, sex, pregnancy, time of day, and laboratory methods. In adults, neutrophils typically comprise about 40–70% of white blood cells, with absolute counts commonly expressed as cells per microliter (e.g., 1.5–8.0 x 10^9/L in many reference ranges). Values outside the normal range can indicate infection, inflammation, stress, medication effects, bone marrow disorders, or other medical conditions.
- High neutrophils (neutrophilia): Often reflect acute bacterial infection, inflammation, tissue injury, stress from surgery or trauma, smoking, corticosteroid use, or certain hematologic conditions. In some cases, high counts persist with chronic inflammation or malignancy. Context and trend over time matter for interpretation.
- Low neutrophils (neutropenia): Increases susceptibility to infections and can arise from bone marrow suppression (chemotherapy, certain drugs, aplastic anemia), severe systemic illness, autoimmune destruction, vitamin deficiencies, or genetic conditions. The risk and clinical approach depend on the degree of neutropenia and accompanying symptoms.
- Diagnostic approach: Interpreting neutrophil counts requires considering the complete blood count (CBC) with differential, patient symptoms, recent illnesses, medications, and underlying medical history. In many cases, repeat testing or additional tests (infection workups, bone marrow evaluation) are guided by the clinical scenario.
- Function and significance: Beyond quantity, neutrophil function (chemotaxis, phagocytosis, degranulation) is crucial for effective host defense. Abnormal function can occur in inherited disorders or acquired conditions, potentially affecting infection risk even with normal counts.
If you’re looking for specific values, interpretation in a particular clinical context, or guidance on what to discuss with a clinician, share details like your age, any current symptoms, and whether you have an upcoming blood test or a current CBC result. I can tailor the explanation and help outline questions to ask your healthcare provider.
