White Blood Cell Count in Lyme Disease
The white blood cell (WBC) count typically remains normal in Lyme disease, and an elevated WBC count should prompt consideration of alternative diagnoses or coinfection with other tick-borne pathogens.
Expected Laboratory Findings in Lyme Disease
- The WBC count is characteristically normal in uncomplicated Lyme disease 1
- Routine laboratory parameters including complete blood counts are generally unremarkable in patients with erythema migrans and early Lyme disease 2
- Unlike many bacterial infections, Lyme disease does not typically trigger leukocytosis, which helps distinguish it from other acute bacterial processes 2
When to Suspect Coinfection
If a patient with suspected or confirmed Lyme disease presents with leukopenia, thrombocytopenia, or persistent high-grade fever (>48 hours despite appropriate antibiotics), strongly consider coinfection with Anaplasma phagocytophilum or Babesia microti. 2, 1
Key Laboratory Clues for Coinfection:
- Leukopenia (present in up to 53% of anaplasmosis cases) suggests Anaplasma phagocytophilum coinfection 2, 1
- Thrombocytopenia (present in up to 94% of anaplasmosis cases) is particularly suggestive of coinfection 2, 1
- Elevated hepatic transaminases with cytopenias point toward anaplasmosis rather than Lyme disease alone 2, 1
- High-grade fever persisting beyond 48 hours despite appropriate Lyme treatment warrants evaluation for coinfection 2, 1
Clinical Context and Diagnostic Approach
- The absence of leukocytosis is actually characteristic of Lyme disease and should not delay diagnosis when clinical features (erythema migrans, appropriate exposure history) are present 2
- In patients with more severe initial symptoms than typically seen with Lyme disease alone, obtain a complete blood count with differential to assess for cytopenias that would suggest coinfection 2, 1
- Coinfection occurs in <10% of Lyme disease patients but is more common in endemic areas where multiple tick-borne pathogens circulate 1
Common Pitfalls to Avoid
- Do not exclude Lyme disease based on a normal WBC count - this is the expected finding and supports rather than refutes the diagnosis 2, 1
- Do not assume all tick-borne illnesses present similarly - while Lyme disease has normal WBC counts, Rocky Mountain spotted fever may show normal or slightly elevated counts with bandemia, and anaplasmosis characteristically causes leukopenia 2
- Do not overlook coinfection in patients with unexplained cytopenias - the presence of leukopenia or thrombocytopenia in a patient with Lyme disease should trigger empiric treatment for anaplasmosis while awaiting confirmatory testing 2, 1