What labs should be ordered for a patient with a tick bite?

Laboratory Tests for Tick Bite Evaluation

For patients with tick bites, laboratory testing should be guided by the specific suspected tick-borne pathogen based on geographic location, tick species, and clinical presentation, rather than routine testing of all patients with tick bites. 1

Initial Approach to Laboratory Testing

• Consultation with the microbiology laboratory is essential to determine specimen requirements, testing availability, and turnaround times 1
• Patient travel history, recent locations, and potential for tick bite duration are critical factors in determining appropriate testing 1
• Laboratory testing should be targeted based on clinical symptoms, as tick-borne diseases often present with nonspecific symptoms including fever, chills, aches, pains, and rashes 1

Specific Laboratory Tests by Suspected Pathogen

Lyme Disease (Borrelia burgdorferi)

• Early Lyme disease with erythema migrans:

  • Clinical diagnosis is sufficient; laboratory testing is insensitive in the first 2 weeks of infection 1
  • No laboratory testing required if classic erythema migrans is present 1

• Early disseminated or late Lyme disease:

  • Two-tier testing approach: EIA IgG and IgM antibody screening followed by Western blot confirmation if EIA is positive or equivocal 1
  • Serum specimens in clot tube, room temperature, ≤2 hours 1
  • For neuroborreliosis: Paired serum/CSF antibody levels (CSF/serum antibody index) 1

Rickettsial Diseases (Rocky Mountain Spotted Fever)

• Acute and convalescent IFA for R. rickettsii IgM and IgG antibodies 1
• NAAT (nucleic acid amplification test) 1
• Immunohistochemical staining of spotted fever group rickettsiae antigens in skin biopsy specimens 1
• Specimens:
  • Serum in clot tube, room temperature, ≤2 hours 1
  • Skin biopsy (preferably from maculopapule with petechiae) in sterile container, transport on ice, ≤1 hour 1

Ehrlichiosis/Anaplasmosis

• Serology: Acute and convalescent IFA titers for Ehrlichia antibodies 1
• NAAT (definitive diagnostic test for E. ewingii) 1
• Immunohistochemical staining of Ehrlichia antigens in tissue specimens 1
• Specimens:
  • Serum in clot tube, room temperature, ≤2 hours 1
  • Whole blood in heparin or EDTA anticoagulant tube, transport on ice, ≤1 hour 1

Babesiosis (Babesia microti)

• Primary test: Giemsa, Wright's, or Wright-Giemsa stains of peripheral thin and thick blood smears (Giemsa preferred) 1
• NAAT for Babesia detection 1
• Serology: Acute and convalescent IFA titers for Babesia antibodies (IgM and IgG) 1
• Specimens:
  • Whole blood for smears (prepare immediately) 1
  • EDTA anticoagulant tube, room temperature, ≤1 hour 1
  • Serum in clot tube, room temperature, ≤2 hours 1

Colorado Tick Fever Virus

• Virus-specific IFA-stained blood smears 1
• Serology: IFA titers or complement fixation 1
• Specimens:
  • Blood in EDTA anticoagulant tube, room temperature, ≤2 hours 1
  • Serum in clot tube, room temperature, ≤2 hours 1

Timing of Laboratory Testing

• For most tick-borne diseases, acute and convalescent serum samples should be collected 1
  • Acute serum: Within 7 days of symptom onset 1
  • Convalescent serum: At least 21 days after symptom onset 1
• Early antibiotic treatment may blunt antibody response, potentially leading to false-negative results 1

Important Considerations and Pitfalls

• Testing patient-retrieved ticks for infections is not recommended as it does not predict human infection 2
• A negative peripheral blood smear does not rule out tick-borne disease due to often low and variable sensitivity 1
• Prophylactic antibiotic treatment should only be considered within 72 hours of removing identified high-risk ticks (Ixodes species attached ≥36 hours in endemic areas) 3, 4
• For high-risk Ixodes bites meeting specific criteria, a single dose of oral doxycycline (200 mg for adults, 4.4 mg/kg up to 200 mg for children ≥8 years) may be given as prophylaxis 3, 4
• Monitor all bite sites for 30 days for signs of infection or development of erythema migrans 3

Emerging Diagnostic Approaches

• Multiplex serologic platforms are being developed to simultaneously test for multiple tick-borne pathogens, which may improve diagnostic accuracy in the future 5
• Consider potential co-infections when evaluating patients with tick bites, as ticks can transmit multiple pathogens simultaneously 6