Causes of Increased Absolute Neutrophils with Increased WBC Count
Bacterial infections are the most common cause of increased absolute neutrophils with elevated WBC counts, with likelihood ratios of 3.7 for WBC >14,000 cells/mm³ and 14.5 for band counts >1,500 cells/mm³. 1
Primary Causes of Neutrophilia with Leukocytosis
Infectious Causes
- Bacterial infections - strongest association with neutrophilia
- Produces neutrophilia with left shift (increased band forms)
- Elevated total band count (>1,500 cells/mm³) has highest likelihood ratio (14.5) for bacterial infection
- Increased percentage of neutrophils (>90%) has likelihood ratio of 7.5
- Increased band neutrophils (>16%) has likelihood ratio of 4.7 1
- Viral infections - typically cause lymphocytosis rather than neutrophilia 2
- Parasitic infections - more commonly associated with eosinophilia 2
Inflammatory Causes
Medication-Related Causes
Physiologic Stress Responses
Hematologic Malignancies
Other Causes
- Asplenia
- Smoking
- Obesity 3
Diagnostic Value of Neutrophilia with Leukocytosis
The presence of an elevated WBC count (>14,000 cells/mm³) or a left shift (percentage of band neutrophils >16% or total band neutrophil count >1,500 cells/mm³) warrants careful assessment for bacterial infection, even in the absence of fever 1.
Key Diagnostic Indicators
- WBC count >14,000 cells/mm³: likelihood ratio 3.7 for bacterial infection
- Band neutrophils >16%: likelihood ratio 4.7
- Neutrophils >90%: likelihood ratio 7.5
- Band count >1,500 cells/mm³: likelihood ratio 14.5 1
Important Clinical Considerations
- High WBC and neutrophil counts strongly suggest bacterial infection, but normal values don't rule it out 5
- Toxic granulation in neutrophils appears to be as sensitive as absolute neutrophil count in predicting bacterial infection 6
- Time-series data of left shift and WBC count reflect real-time neutrophil consumption during bacterial infection, allowing more accurate evaluation 7
Special Populations
- Band count has greater sensitivity for detecting bacterial infections in infants and elderly patients compared to other age groups 6
- Age-specific normal ranges should be used when interpreting WBC counts 3
Warning Signs
- WBC counts above 100,000/mm³ represent a medical emergency due to risk of brain infarction and hemorrhage 4
- Concurrent abnormalities in red blood cell or platelet counts, weight loss, bleeding/bruising, organomegaly, or immunosuppression should raise suspicion for primary bone marrow disorders 4
When evaluating increased absolute neutrophils with increased WBC count, bacterial infection should be the first consideration, but the clinical context, medication history, and presence of physiologic stressors must be carefully assessed to determine the underlying cause.