What are the typical complete blood count (CBC) findings in patients with Lyme disease?

CBC Findings in Lyme Disease

In Lyme disease, the complete blood count (CBC) is typically normal or shows only mild abnormalities, with the most common findings being a slightly elevated white blood cell count or mild anemia. 1

Common CBC Findings

White Blood Cell (WBC) Count

• Usually normal or slightly elevated
• Atypical lymphocytes may sometimes be present 1
• Unlike in Human Granulocytic Anaplasmosis (HGA), Lyme disease rarely causes leukopenia 1, 2

Platelet Count

• Generally remains within normal range
• No significant thrombocytopenia (unlike in HGA or other tick-borne diseases) 1, 2

Hemoglobin

• Usually normal
• Mild anemia may be present in some cases

Comparison with Other Tick-Borne Diseases

It's important to distinguish Lyme disease from other tick-borne illnesses based on CBC findings:

• Human Granulocytic Anaplasmosis (HGA):

  • Leukopenia (low WBC count)
  • Thrombocytopenia (low platelet count)
  • Elevated liver enzymes
  • More severe illness presentation than Lyme disease 1, 2

• Ehrlichiosis:

  • Leukopenia with left shift (increased bands)
  • Thrombocytopenia (often severe)
  • Anemia 1

CBC Findings by Stage of Lyme Disease

Early Localized Lyme Disease

• CBC typically normal
• Minimal or no hematologic abnormalities

Early Disseminated Lyme Disease

• May show mild leukocytosis
• Transcriptome analysis shows significant interferon-regulated gene expression 3
• Otherwise, CBC parameters often remain within normal limits

Late Disseminated Lyme Disease

• CBC usually remains normal
• Hematologic abnormalities are not characteristic features

Clinical Relevance

The lack of significant CBC abnormalities in Lyme disease is clinically important:

1. A normal CBC does not exclude Lyme disease
2. Significant CBC abnormalities (especially leukopenia and thrombocytopenia) should prompt consideration of co-infection with other tick-borne pathogens
3. CBC monitoring is not typically used to assess treatment response in Lyme disease

Diagnostic Considerations

When evaluating a patient with suspected Lyme disease:

• CBC findings alone are not diagnostic
• Serologic testing remains the mainstay of laboratory diagnosis 1
• The presence of significant CBC abnormalities should raise suspicion for co-infections or alternative diagnoses

Common Pitfalls

• Attributing significant CBC abnormalities to Lyme disease alone
• Failing to consider co-infections when CBC shows leukopenia or thrombocytopenia
• Over-relying on CBC findings for diagnosis or treatment monitoring
• Misinterpreting mild, non-specific CBC changes as evidence of active Lyme infection

In summary, while CBC findings in Lyme disease are generally unremarkable, understanding the typical pattern helps differentiate it from other tick-borne diseases that may present with more pronounced hematologic abnormalities.