What is the appropriate workup for a patient with leukocytosis (elevated White Blood Cell count)?

Evaluation of Leukocytosis (WBC 13.5)

A white blood cell count of 13.5 is mildly elevated and requires a systematic evaluation focused on identifying common infectious and non-infectious causes while ruling out more serious hematologic disorders.

Initial Assessment

• Complete Blood Count with Differential

  • Assess neutrophil, lymphocyte, monocyte, eosinophil, and basophil percentages
  • Look for left shift (increased band forms/immature neutrophils) suggesting bacterial infection 1
  • Evaluate for presence of blasts or abnormal cells on peripheral smear

• Clinical Context Evaluation

  • Assess for fever, chills, localized pain, or other signs of infection
  • Document recent stressors (physical/emotional), medications, and underlying conditions
  • Note any constitutional symptoms (weight loss, night sweats, fatigue) that might suggest malignancy 2

Interpretation Based on Differential Count

Neutrophilia-Predominant Leukocytosis

• Bacterial infections: Pneumonia, UTI, skin/soft tissue infections, abscesses
• Inflammatory conditions: Rheumatologic disorders, tissue injury, post-surgical state
• Medications: Corticosteroids, lithium, beta-agonists 3
• Physiologic stress: Exercise, seizures, pain, emotional stress

Lymphocytosis-Predominant Leukocytosis

• Viral infections: EBV, CMV, HIV, viral hepatitis
• Chronic lymphocytic leukemia (especially if persistent)
• Pertussis (whooping cough)

Eosinophilia-Predominant Leukocytosis

• Allergic reactions: Asthma, drug reactions, atopic dermatitis
• Parasitic infections: Helminth infections
• Hematologic disorders: Hypereosinophilic syndromes

Diagnostic Approach

1. If infectious etiology suspected:

   • Targeted cultures (blood, urine, sputum) based on symptoms
   • Chest X-ray if respiratory symptoms present
   • Urinalysis if urinary symptoms present

2. If non-infectious etiology suspected:

   • Review medication list for potential causes
   • Basic metabolic panel, liver function tests
   • Inflammatory markers (ESR, CRP)

3. If hematologic disorder suspected (based on very high WBC, abnormal cells on smear, or other cytopenias):

   • Consultation with hematology
   • Consider bone marrow aspiration and biopsy

Special Considerations

• Severity Assessment: WBC counts >35,000/μL are considered extreme leukocytosis with higher mortality risk (16-33%) 4
• Urgent Evaluation: WBC counts >100,000/μL represent a medical emergency due to risk of leukostasis, brain infarction, and hemorrhage 3
• Age-Specific Norms: Use age-appropriate reference ranges, especially in children and pregnant women 2

When to Refer to Hematology

• Persistent unexplained leukocytosis after initial workup
• Presence of abnormal cells on peripheral smear
• Concurrent abnormalities in red blood cell or platelet counts
• Constitutional symptoms suggesting malignancy
• WBC count >35,000/μL without clear infectious cause 2, 5

Follow-up Recommendations

• For mild leukocytosis (as in this case with WBC 13.5) with identified infectious or inflammatory cause:

  • Treat underlying condition
  • Repeat CBC in 2-4 weeks to document normalization
  • If persistent elevation, consider expanded workup

• For unexplained leukocytosis:

  • Repeat CBC with manual differential in 1-2 weeks
  • Consider hematology consultation if persistent or worsening

A WBC count of 13.5 is only mildly elevated and most commonly represents a benign reactive process, but should be evaluated in clinical context to rule out more serious conditions that could affect morbidity and mortality.