What are the common causes of neutrophilia in a patient with no significant past medical history?

Causes of Neutrophilia

Bacterial infection is the most common cause of neutrophilia in patients with no significant past medical history, particularly when accompanied by a left shift (elevated band count >1500 cells/mm³). 1

Infectious Causes (Most Common)

Bacterial infections are the primary driver of neutrophilic leukocytosis and should be your first consideration: 1

• Common bacterial pathogens include coagulase-negative staphylococci, Staphylococcus aureus, and Escherichia coli 1
• Septicemia produces high-grade leukocytosis (WBC >20,000 cells/mm³) with left shift and carries increased mortality risk 1
• Severity markers help confirm bacterial infection:
  • Neutrophil percentage >90% has a likelihood ratio of 7.5 for bacterial infection 1
  • Band neutrophils >16% has a likelihood ratio of 4.7 for bacterial infection 1
  • Total band count >1500 cells/mm³ strongly suggests documented bacterial infection 1

Inflammatory Causes (Non-infectious)

Systemic inflammatory disorders are the second major category to consider: 1

• Adult-onset Still's disease (AOSD) produces striking neutrophilia, with 50% of patients having WBC >15,000 cells/L and 37% having WBC >20,000 cells/L 1
• Vasculitis and connective tissue diseases can cause neutrophilic leukocytosis 1
• Malignancy, particularly solid tumors that are necrotic or causing obstruction, may produce neutrophilia 1

Recovery from Neutropenia

Reactive leukocytosis can occur when neutrophil counts recover from severe neutropenia (<500 cells/mm³), especially in the setting of infection 1

Clinical Approach

When evaluating neutrophilia in a patient with no significant past medical history, prioritize the following:

1. Look for infection first: Examine for fever, localizing symptoms, and signs of bacterial infection (though these may be subtle) 2
2. Check the differential: Calculate absolute band count and neutrophil percentage to assess severity 1
3. Consider inflammatory conditions: If infection is ruled out, evaluate for systemic inflammatory disorders like AOSD, particularly if WBC is markedly elevated 1
4. Evaluate for malignancy: In the absence of infection or inflammatory disease, consider occult malignancy, especially if neutrophilia persists 1

Common Pitfall

Do not dismiss neutrophilia as "reactive" without identifying the underlying cause—bacterial infection requires prompt treatment, and missing septicemia can be fatal given its association with increased mortality when WBC >20,000 cells/mm³. 1