What laboratory tests are recommended for a patient presenting after a tick bite?

Laboratory Tests for Tick Bite Evaluation

For patients presenting after a tick bite, laboratory testing is generally not recommended unless symptoms develop, as testing asymptomatic individuals leads to false results and unnecessary treatment. 1

Initial Assessment

When evaluating a patient with a tick bite, focus on:

1. Tick identification: Determine if it was an Ixodes species vector tick 2
2. Geographic risk: Assess if bite occurred in a highly endemic area 2
3. Duration of attachment: Determine if tick was attached for ≥36 hours 2, 1

Laboratory Testing Recommendations

For Asymptomatic Patients:

• No laboratory testing is recommended for asymptomatic individuals following tick bites 2, 1
• Testing immediately after a tick bite is not useful as antibodies take weeks to develop 1
• Testing ticks for infection is not recommended as results don't reliably predict human infection 2, 1

For Symptomatic Patients:

If symptoms develop after a tick bite, appropriate testing may include:

1. For suspected Lyme disease:

   • Two-tier testing (EIA followed by Western blot) for patients with symptoms beyond erythema migrans 2, 1
   • For classic erythema migrans in endemic areas, clinical diagnosis without testing is sufficient 1

2. For suspected rickettsial diseases:

   • Blood collection in heparin or citrate tubes (not EDTA) for culture 2
   • EDTA tubes for molecular diagnosis 2
   • Serological testing with acute and convalescent sera (2-4 weeks apart) 2
   • Microimmunofluorescence (MIF) is the reference method for serological diagnosis 2

3. For suspected anaplasmosis/ehrlichiosis:

   • Blood smears with Wright's, Giemsa or Diff-Quik stains 2
   • PCR testing of blood or serum 2
   • Serologic testing with paired acute and convalescent samples 2

Timing of Sample Collection

• Acute samples: Collect before antimicrobial therapy when possible 2
• Convalescent samples: Collect 2-4 weeks after initial presentation 2
• For rickettsial diseases, if a four-fold rise in antibody titer is not observed, a third sample after 4-6 weeks may be considered 2

Common Pitfalls to Avoid

• Premature testing: Testing immediately after a tick bite leads to false negatives as antibodies take weeks to develop 1
• Testing asymptomatic patients: Leads to false positives or detection of previous infections 1, 3
• Overreliance on serology: In early Lyme disease with erythema migrans, serology is often negative and unnecessary 2, 1
• Inappropriate prophylaxis: Antibiotic prophylaxis should only be given for high-risk tick bites meeting all three criteria (Ixodes species, endemic area, ≥36 hours attachment) 2, 1

Monitoring Recommendations

Monitor patients for 30 days after tick bite for development of:

• Erythema migrans (expanding rash)
• Fever
• Headache
• Muscle/joint pain
• Fatigue 1

If symptoms develop, appropriate testing as outlined above should be performed based on the specific clinical presentation.