What is the protocol for a blood test after a tick bite to check for tick-borne illnesses such as Lyme disease?

Blood Test Protocol After Tick Bite for Tick-Borne Illnesses

Routine blood testing immediately after a tick bite is NOT recommended for asymptomatic individuals, as antibodies take weeks to develop and early testing leads to false negatives. 1

Initial Assessment After Tick Bite

1. Document and assess the tick bite:

   • Identify the tick species (if available)
   • Estimate attachment duration
   • Note geographic location of exposure
   • Record time since tick removal 1

2. Risk stratification based on:

   • Tick species (Ixodes ticks pose highest risk for Lyme disease)
   • Attachment duration (≥36 hours increases risk)
   • Geographic location (endemic areas have higher risk)
   • Degree of engorgement of the tick 2, 1

Laboratory Testing Protocol

For Asymptomatic Individuals:

• No laboratory testing is recommended following tick bites in asymptomatic individuals 1
• Monitor for 30 days for development of symptoms 1

For Symptomatic Individuals:

If symptoms develop (fever, headache, rash, myalgias), the following tests are recommended:

1. Initial laboratory tests:

   • Complete blood count (CBC) with differential
   • Liver function tests
   • Serological testing for tick-borne diseases 1

2. Lyme disease testing (two-tier approach):

   • First tier: Enzyme-linked immunosorbent assay (ELISA) or immunofluorescence assay (IFA)
   • Second tier: Western blot confirmation if first tier is positive 1

3. Additional testing based on clinical suspicion:

   • PCR testing of whole blood for early diagnosis of rickettsial diseases
   • Examination of peripheral blood smears for morulae in leukocytes (low sensitivity: 1-20%) 1

Timing of Antibody Detection

Time Post-Bite	Antibody Detection Sensitivity
0-7 days	Generally negative and insensitive
7-15 days	Both IgM and IgG antibodies usually detectable
2-3 weeks	Highest sensitivity for antibody detection
Months to years	Antibodies can remain detectable even after successful treatment [1]

Important Considerations

• IgM and IgG antibodies are typically not detectable before the second week of illness 1
• Convalescent serology is recommended 2-4 weeks post-bite for confirmation 1
• Blood collection should use appropriate tubes:
  • Heparin or citrate tubes for culture
  • EDTA tubes for molecular diagnosis (PCR) 1

Prophylactic Treatment

Antibiotic prophylaxis may be considered instead of testing when all these criteria are met:

• The tick can be identified as an adult or nymphal Ixodes scapularis
• Estimated attachment duration ≥36 hours
• Local infection rate of ticks with B. burgdorferi is ≥20%
• Prophylaxis can start within 72 hours of tick removal 2, 1

When indicated, a single dose of doxycycline is recommended:

• Adults: 200 mg
• Children ≥8 years: 4 mg/kg (maximum 200 mg) 2, 1

Common Pitfalls to Avoid

• Testing immediately after a tick bite (leads to false negatives) 1
• Relying solely on patient's estimate of attachment duration (usually underestimated) 2
• Assuming absence of tick bite history excludes tick-borne disease (up to 40% of patients with Rocky Mountain Spotted Fever don't report tick bites) 1
• Failing to consider geographic risks and endemic diseases in your region 1
• Overinterpreting positive B. burgdorferi DNA in a tick as proof of future Lyme disease 3

Remember that if clinical suspicion is high for tick-borne disease, appropriate antibiotic therapy should be started while awaiting test results 1.