What other basic blood work is important to reference with a lab result of neutrophilia?

Basic Blood Work to Reference with Neutrophilia (65% Neutrophils)

When evaluating a patient with neutrophilia (65% neutrophils), a complete blood count with differential, C-reactive protein, and comprehensive metabolic panel should be ordered to properly assess for potential bacterial infection and other underlying causes. 1

Understanding Neutrophilia

Neutrophilia is characterized by an increased percentage of neutrophils in the blood, with normal values typically ranging from 45-75%. A value of 65% is at the higher end of normal range, suggesting a potential early neutrophilic response that warrants further investigation.

Key Blood Tests to Order:

1. Complete Blood Count (CBC) with Differential

   • Total White Blood Cell (WBC) count
   • Absolute Neutrophil Count (ANC)
   • Band neutrophil percentage (immature neutrophils)
   • Lymphocyte count
   • Monocyte count
   • Eosinophil count
   • Platelet count
   • Hemoglobin and hematocrit

2. Inflammatory Markers

   • C-reactive protein (CRP)
   • Erythrocyte sedimentation rate (ESR)

3. Comprehensive Metabolic Panel

   • Liver function tests (AST, ALT, alkaline phosphatase, bilirubin)
   • Renal function (creatinine, BUN)
   • Electrolytes

Clinical Significance and Interpretation

Bacterial Infection Assessment

• The combination of neutrophilia with an elevated WBC count (>14,000 cells/mm³) provides strong evidence for bacterial infection 1
• Look specifically for band neutrophils (left shift) - a band count >1,500 cells/mm³ has a likelihood ratio of 14.5 for bacterial infection 1
• Neutrophils >90% have a likelihood ratio of 7.5 for bacterial infection 1

Additional Findings to Note

• Presence of toxic granulation in neutrophils appears to be as sensitive as ANC in predicting bacterial infections 2
• Morphological changes in neutrophils (toxic granulation, vacuolation, Döhle bodies) should be evaluated on peripheral blood smear 2
• Thrombocytopenia in conjunction with neutrophilia may indicate more severe disease with potential organ dysfunction 1

Special Considerations

Age-Related Differences

• Band count has greater sensitivity for detecting bacterial infections in infants and elderly patients compared to other age groups 2
• In elderly patients, fever may be absent despite serious infection, making laboratory values more critical 1

Potential Causes Beyond Infection

Neutrophilia can result from:

• Bacterial infections
• Inflammatory conditions
• Stress response
• Corticosteroid use
• Hematologic disorders
• Certain medications

Diagnostic Algorithm

1. If neutrophilia (65%) is present with:

   • WBC >14,000 cells/mm³ → High suspicion for bacterial infection
   • Band neutrophils >16% → Very high suspicion for bacterial infection
   • Normal WBC count → Consider stress, medications, or early/resolving infection

2. If bacterial infection is suspected:

   • Obtain appropriate cultures (blood, urine, sputum, etc.) based on clinical presentation
   • Consider imaging studies directed at potential infection sites

3. If neutrophilia persists without evidence of infection:

   • Consider medication effects
   • Evaluate for inflammatory disorders
   • Consider hematology consultation if persistent

Pitfalls and Caveats

• Relying solely on neutrophil percentage without considering absolute counts can be misleading
• Failure to check for band neutrophils may miss early bacterial infections
• Overreliance on laboratory values without clinical correlation can lead to inappropriate antibiotic use
• Neutrophilia can be a normal response to stress, exercise, or certain medications, requiring clinical correlation

By systematically evaluating these laboratory parameters alongside clinical findings, clinicians can more accurately determine the significance of neutrophilia and guide appropriate management decisions.