What does a high neutrophil count mean?

High Neutrophil Count: Clinical Significance and Evaluation

A high neutrophil count (neutrophilia) most strongly indicates an underlying bacterial infection, with an elevated total neutrophil count (>14,000 cells/mm³) having a likelihood ratio of 3.7 for detecting bacterial infection, even in the absence of fever. 1

Definition and Diagnostic Criteria

Neutrophilia is characterized by the following parameters:

• Total white blood cell (WBC) count >14,000 cells/mm³
• Neutrophil percentage >90%
• Elevated total band count >1,500 cells/mm³
• Increased percentage of band neutrophils >16% (left shift) 2, 1

Of these parameters, an elevated total band count (>1,500/mm³) has the highest likelihood ratio (14.5) for detecting bacterial infection, while an increase in the percentage of neutrophils (>90%) and band neutrophils (>16%) have likelihood ratios of 7.5 and 4.7, respectively. 2, 1

Clinical Significance

Neutrophilia typically indicates:

1. Bacterial Infection

• High probability of underlying bacterial infection even without fever 2
• Particularly significant in elderly patients where fever may be absent despite infection 2
• Severe infections affecting the lungs, skin, or viscera are common presentations 2

2. Inflammatory Response

• Neutrophils are critical effectors in the acute inflammatory response 3
• They accumulate rapidly at sites of tissue injury 4
• Play vital roles in phagocytosis and bacterial killing 5

3. Other Conditions

• Chronic inflammatory diseases (atherosclerosis, diabetes mellitus, nonalcoholic fatty liver disease) 6
• Autoimmune disorders 6
• Stress response
• Certain medications (corticosteroids, lithium)

Evaluation Approach

When neutrophilia is detected, the following approach is recommended:

1. Confirm the finding with repeat complete blood count with differential, preferably with manual differential to assess bands and immature forms 2

2. Assess for signs of infection:

   • Careful assessment for bacterial infection is warranted in any patient with elevated WBC count or left shift, with or without fever 2
   • Look for focal signs of infection (respiratory, urinary, skin, abdominal)
   • Obtain appropriate cultures before initiating antimicrobial therapy 1

3. Further diagnostic workup based on clinical presentation:

   • If suspected bacterial infection: appropriate site-specific cultures 2
   • If persistent neutrophilia without clear source: consider bone marrow examination 3
   • Flow cytometry may be necessary in cases where hematologic disorders are suspected 1

Clinical Implications and Management

The management approach depends on the underlying cause:

• For bacterial infection: Prompt initiation of appropriate antibiotics based on likely source and severity 1

  • High-risk patients (hemodynamically unstable, significant comorbidities) require immediate broad-spectrum IV antibiotics 1
  • Low-risk patients may be considered for oral antibiotics if stable 1

• For chronic inflammatory conditions: Address the underlying disorder

• For medication-induced neutrophilia: Consider medication review and possible adjustment

Common Pitfalls to Avoid

1. Ignoring neutrophilia in the absence of fever, especially in elderly patients where bacterial infections may present without fever 2

2. Delaying empiric antibiotic therapy in suspected infection with neutrophilia 1

3. Failing to obtain appropriate cultures before initiating antimicrobial therapy 1

4. Overlooking non-infectious causes of neutrophilia such as chronic inflammatory conditions, medications, or stress response

5. Misinterpreting asymptomatic bacteriuria as UTI in elderly patients with neutrophilia (high prevalence of 15-50% in non-catheterized long-term care facility residents) 2