High Neutrophil Count: Meaning and Clinical Significance
A high neutrophil count (neutrophilia) most commonly indicates an active bacterial infection, but can also signal inflammation, stress, certain medications, or more serious bone marrow disorders. The clinical significance depends on the degree of elevation, presence of immature forms, and associated symptoms.
Definition and Normal Values
According to clinical guidelines, neutrophilia is defined as:
- In bronchoalveolar lavage fluid: >3% neutrophils indicates neutrophilia 1
- In peripheral blood: >14,000 cells/mm³ is considered leukocytosis with likely neutrophil predominance 1
Common Causes of Neutrophilia
1. Infections
- Bacterial infections are the most common cause of neutrophilia 1, 2
- Approximately 50-60% of febrile neutropenic patients have an established or occult infection 1
- Primary sites of infection often include:
- Alimentary tract (mouth, pharynx, esophagus, bowel)
- Sinuses
- Lungs
- Skin 1
2. Inflammatory Conditions
- Non-infectious inflammatory processes can trigger neutrophilia
- Examples include:
- Autoimmune disorders
- Tissue injury
- Post-surgical inflammation 2
3. Physiologic Stress
- Physical stress (seizures, anesthesia, overexertion)
- Emotional stress
- Both can elevate white blood cell counts, particularly neutrophils 2
4. Medication Effects
- Corticosteroids
- Lithium
- Beta-agonists
- These medications commonly cause neutrophilia 2
5. Primary Bone Marrow Disorders
- Acute leukemias
- Chronic leukemias
- Myeloproliferative disorders
- These should be suspected with extremely elevated counts or abnormalities in other blood cell lines 2
Clinical Significance of Neutrophilia
Diagnostic Value
- An elevated neutrophil count (>14,000 cells/mm³) has a likelihood ratio of 3.7 for bacterial infection 1
- The presence of a "left shift" (increased immature neutrophils or bands >16%) has a likelihood ratio of 4.7 for bacterial infection 1
- An elevated total band count (>1500 cells/mm³) has the highest likelihood ratio (14.5) for detecting bacterial infection 1
Prognostic Value
- In cancer patients, the frequency and severity of infection are inversely proportional to neutrophil count 1
- Highest risk of severe infection occurs when neutrophil count is <100/mcL 1
- In long-term care facility residents, leukocytosis has been associated with increased mortality in:
- Nursing home-acquired pneumonia (WBC >15,000 cells/mm³)
- Bloodstream infection (WBC >20,000 cells/mm³) 1
- In cardiovascular disease, elevated neutrophil counts correlate with higher risk of major adverse cardiac events 3
When to Be Concerned
Red Flags
- White blood cell counts above 100,000/mm³ represent a medical emergency due to risk of brain infarction and hemorrhage 2
- Concurrent abnormalities in red blood cell or platelet counts
- Weight loss, bleeding or bruising
- Liver, spleen or lymph node enlargement
- Immunosuppression 2
Monitoring Considerations
- Single time-point measurements may be misleading
- Time-series data of left shift and WBC count better reflect real-time neutrophil consumption during infection 4
- Dynamic changes in WBC count and left shift reflect the progression from mild to serious bacterial infection 4
Clinical Approach
When neutrophilia is detected:
- Evaluate for signs and symptoms of infection
- Review medication list for potential causes
- Consider recent stressors or inflammatory conditions
- If extremely elevated or accompanied by abnormalities in other cell lines, consider bone marrow disorders
- Monitor trends over time rather than relying on a single measurement 4
In the absence of fever, leukocytosis, left shift, or specific clinical manifestations of a focal infection, additional diagnostic tests may not be indicated due to low potential yield 1.