Would a complete blood count (CBC) show an elevation in white blood cells in a patient with cellulitis of the lower extremity?

White Blood Cell Elevation in Lower Extremity Cellulitis

Yes, a CBC will typically show an elevation in white blood cells in a patient with cellulitis of the lower extremity, with approximately 69-77% of patients demonstrating leukocytosis.

Laboratory Findings in Cellulitis

Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue that commonly affects the lower extremities. The systemic inflammatory response to this infection often manifests in laboratory values:

• White Blood Cell Count:

  • Leukocytosis (elevated WBC count) is present in approximately 69-77% of patients with cellulitis 1, 2
  • Mean neutrophil ratio of approximately 79.7% in patients with cellulitis 1
  • Left shift (increased band neutrophils) is commonly observed 3

• Inflammatory Markers:

  • C-reactive protein (CRP) is elevated in approximately 76.1% of cellulitis cases 4
  • Elevated inflammatory markers may persist longer in patients with recurrent cellulitis 5

Clinical Correlation

The presence of leukocytosis correlates with several clinical factors:

• Severity: Higher WBC counts (≥15,000 cells/mm³) may indicate more severe infection or specific pathogens 6, 7
• Systemic Involvement: Frequently associated with systemic symptoms such as fever, which is present in approximately 77.3% of cases 1
• Diagnostic Value: An elevated WBC count has a likelihood ratio of 3.7 for bacterial infection 3
• Pathogen Correlation: Very high WBC counts (≥15,000 cells/mm³) may suggest specific pathogens like Haemophilus influenzae, though this is more common in facial cellulitis 6, 7

Diagnostic Considerations

When evaluating a patient with suspected lower extremity cellulitis:

• A complete blood count with differential should be performed within 12-24 hours of symptom onset 2
• The presence of a left shift (band neutrophils >6% or band count >1,500 cells/mm³) is a powerful diagnostic indicator with a likelihood ratio of 14.5 for bacterial infection 3
• Blood cultures are typically positive in only 5-11.4% of cellulitis cases 2, 4, but should be considered in patients with:
  • High fever
  • Systemic toxicity
  • Immunocompromise
  • Lymphedema (higher risk of bacteremia)

Pitfalls and Caveats

• Normal WBC Count: A normal WBC count does not rule out cellulitis, as some patients may have cellulitis without leukocytosis
• Immunocompromised Patients: May not mount a typical inflammatory response, resulting in normal WBC counts despite significant infection
• Differential Diagnosis: Other conditions can cause both erythema and leukocytosis (e.g., deep vein thrombosis, contact dermatitis with secondary infection)
• Recurrent Episodes: Patients with recurrent cellulitis may have more pronounced laboratory abnormalities, including higher WBC counts and CRP levels 5

Management Implications

The presence of leukocytosis in a patient with cellulitis may influence management decisions:

• Patients with high WBC counts may require more aggressive treatment or closer monitoring
• Empiric antibiotic therapy should target the most likely pathogens (Streptococci and Staphylococcus aureus) 2
• Serial CBC monitoring can help assess response to therapy 3

In conclusion, while not universally present, leukocytosis is a common finding in patients with lower extremity cellulitis and serves as a useful diagnostic and prognostic marker when interpreted in the context of the clinical presentation.