From the Guidelines
Elevated neutrophil counts, known as neutrophilia, can occur due to several causes, with infections being the most common reason, particularly bacterial infections which trigger the body to produce more neutrophils to fight pathogens. The causes of elevated neutrophil counts can be broken down into several categories, including:
- Infections, such as bacterial infections, which trigger the body to produce more neutrophils to fight pathogens 1
- Inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease, and vasculitis, which can increase neutrophil production
- Physical or emotional stress, which activates the fight-or-flight response, causing neutrophils to be released from bone marrow reserves
- Certain medications, including corticosteroids (prednisone, dexamethasone), lithium, and some antibiotics, which can elevate neutrophil counts
- Hematologic disorders, such as myeloproliferative disorders and leukemia, which may cause abnormal neutrophil production
- Tissue damage from burns, heart attacks, or surgery, which triggers inflammation that increases neutrophil counts
- Smoking, which directly stimulates bone marrow to produce more neutrophils
- Pregnancy, especially in later stages, which naturally elevates neutrophil counts
- Some genetic conditions, such as Down syndrome, which can be associated with higher neutrophil counts
- Cancer, particularly when metastasized, which can stimulate neutrophil production through inflammatory cytokines 1. It is essential to consider these potential causes and seek appropriate medical evaluation to determine the underlying reason for neutrophilia, as the frequency and severity of infection are inversely proportional to the neutrophil count, and the risks of severe infection and bloodstream infection are greatest when the neutrophil count is less than 100/mcL 1.
From the Research
Causes of Elevated Neutrophil Count
Elevated neutrophil count, also known as neutrophilia, can be caused by various factors, including:
- Infections, such as bacterial or viral infections, which can trigger an increase in neutrophil production 2, 3, 4, 5, 6
- Inflammatory conditions, such as arthritis or gout, which can cause an increase in neutrophil count
- Tissue damage or injury, which can lead to an increase in neutrophil production
- Certain medications, such as corticosteroids, which can cause an increase in neutrophil count
- Cancers, such as leukemia, which can affect neutrophil production
Role of Neutrophils in Infections
Neutrophils play a crucial role in controlling bacterial and fungal infections, and their function in antiviral immunity is being increasingly studied 2, 3, 5, 6. They can contribute to pathogen clearance through various mechanisms, including:
- Phagocytosis, which involves the ingestion and destruction of pathogens
- Degranulation, which involves the release of enzymes and antimicrobial peptides
- Neutrophil extracellular traps (NETs), which involve the release of DNA and proteins to trap and kill pathogens
Distinguishing Between Bacterial and Viral Infections
Distinguishing between bacterial and viral infections can be challenging, but serum measurements of human neutrophil lipocalin (HNL) may be a useful diagnostic tool 4. HNL levels can be elevated in both bacterial and viral infections, but the conformation of HNL may differ between the two types of infections. Monomeric HNL is elevated in viral infections, while dimeric HNL is elevated in bacterial infections.