What is the initial evaluation for a child bitten by a tick?

Initial Laboratory Evaluation for Tick Bites in Children

For a 10-year-old boy with a tick bite, initial laboratory testing should include complete blood count (CBC) with differential, liver function tests, and serological testing for tick-borne rickettsial diseases, with PCR testing of whole blood if symptoms are present. 1, 2

Initial Assessment Algorithm

1. Clinical History Assessment

   • Determine tick attachment duration (≥36 hours increases risk)
   • Assess for symptoms (fever, headache, rash, myalgias)
   • Document geographic location of exposure
   • Note time since tick bite occurred

2. Laboratory Testing Based on Presentation:

   A. Asymptomatic Child with Tick Bite

   • No laboratory testing is recommended for asymptomatic individuals following tick bites 2
   • Monitor for 30 days for development of symptoms

   B. Symptomatic Child with Tick Bite

   • Complete blood count (CBC) with differential
     • Look for thrombocytopenia, leukopenia 1, 2
   • Comprehensive metabolic panel
     • Focus on liver enzymes (AST, ALT) 1, 2
   • Serological testing for rickettsial diseases
     • Collect acute serum sample 1
   • PCR testing of whole blood for early diagnosis 2
   • Blood cultures if fever present

Timing of Laboratory Testing

The timing of laboratory testing is crucial as false negatives are common in early testing:

• 0-7 days post-bite: Serological tests generally negative and insensitive 2
• 7-15 days post-bite: Both IgM and IgG antibodies usually detectable 2
• 2-4 weeks post-bite: Convalescent serology recommended for confirmation 1, 2

Important Considerations

• Do not delay treatment for test results: If clinical suspicion is high for tick-borne disease, start appropriate antibiotic therapy (typically doxycycline) while awaiting test results 1, 2

• Recognize limitations: Up to 40% of patients with Rocky Mountain Spotted Fever (RMSF) do not report a history of tick bite, so absence of known tick exposure should not exclude testing when clinically indicated 1

• Avoid unnecessary testing: Testing ticks themselves or asymptomatic patients is not recommended 2

• Consider geographic risks: Different tick-borne diseases are endemic to different regions, which should guide testing choices 1

Common Pitfalls to Avoid

1. Waiting for positive serology before treatment: IgM and IgG antibodies are typically not detectable before the second week of illness; therefore, serology will not be useful in diagnosing infection in its earliest stages 1

2. Relying on tick identification: Most people do not realize they were bitten by a tick, so identification of the specific tick is often not possible and should not delay evaluation 3

3. Missing the diagnosis due to nonspecific symptoms: Tick-borne diseases often begin with non-specific flu-like symptoms that can be misdiagnosed as viral illnesses 4

4. Overlooking severe presentations in children: While often mild, tick-borne illnesses can cause severe manifestations in children, including central nervous system involvement 5

5. Focusing only on Lyme disease: Multiple tick-borne pathogens may co-exist in the same geographic area, requiring consideration of various diseases 1

Remember that between 24-48 hours of tick attachment is typically required for most disease transmission, but monitoring should continue for a full 30 days after the bite 2, 4.