What labs and treatment are recommended for a patient with a cat bite, considering their age, immune status, and underlying medical conditions?

Laboratory Testing for Cat Bites

Routine laboratory testing is generally not required for cat bite wounds unless there is clinical suspicion of systemic infection, retained foreign body, or deep structural involvement. 1

When Laboratory Testing is NOT Needed

• Most uncomplicated cat bites do not require any laboratory workup 1
• Clean, superficial wounds without signs of infection can be managed with wound care and prophylactic antibiotics alone 2, 3
• Laboratory studies add unnecessary cost and delay treatment in straightforward cases 1

When Laboratory Testing IS Indicated

Blood Work

• Complete blood count (CBC) if systemic infection is suspected (fever, chills, malaise, rapidly spreading erythema) 4
• Blood cultures should be obtained if the patient appears septic or has signs of bacteremia 4, 5
• Basic metabolic panel for patients with systemic infection, particularly elderly or those with comorbidities who may develop complications like acute kidney injury 4

Wound Cultures

• Aerobic and anaerobic cultures from the wound should be obtained if:
  • The wound is already infected at presentation 5
  • There is purulent drainage 3
  • The patient has failed initial antibiotic therapy 3
  • Deep tissue involvement is suspected 5
• Cultures help guide antibiotic therapy, though empiric treatment should not be delayed while awaiting results 5
• Gram stain can provide rapid preliminary information about bacterial pathogens 6

Imaging Studies

• Plain radiographs are indicated when:
  • Bites are near bones or joints to evaluate for periosteal penetration, fracture, or foreign body 2, 1
  • There is suspicion of osteomyelitis (pain disproportionate to injury, bony tenderness) 2
  • Retained foreign material (tooth fragments) is suspected 1
• MRI or CT may be needed for suspected deep abscess, septic arthritis, or osteomyelitis 2

Special Populations Requiring More Extensive Workup

Immunocompromised Patients

• Lower threshold for obtaining blood cultures and inflammatory markers 2
• Consider testing for atypical presentations of Bartonella (cat scratch disease) 6, 2
• More aggressive monitoring due to impaired immune response 2

Diabetic Patients

• Vascular assessment to evaluate arterial supply to the affected limb 2
• Consider inflammatory markers (ESR, CRP) to monitor response to therapy 2
• Lower threshold for imaging to rule out deep infection 2

Hand Wounds

• Radiographs are strongly recommended due to high risk of septic arthritis, osteomyelitis, and tendonitis 2, 3
• Consider early surgical consultation for deep hand bites even without obvious infection 3

Additional Mandatory Assessments (Not Laboratory Tests)

• Tetanus immunization status must be evaluated and updated if needed 2, 7, 1
• Rabies risk assessment for scratches/bites from unknown or feral cats 2, 1
• Neurovascular examination documenting pulses, sensation, and range of motion 1

Common Pitfalls to Avoid

• Do not delay empiric antibiotic therapy while waiting for culture results—Pasteurella multocida is present in 75% of cat bites and requires immediate coverage 3, 8, 5
• Do not rely on negative initial cultures to rule out infection, as cat bite infections can develop rapidly (within 3 hours) 5
• Do not underestimate hand wounds—these have the highest infection risk and complication rates 7

Treatment Approach

Amoxicillin-clavulanate 875/125 mg twice daily is the first-line empiric therapy regardless of laboratory results, providing excellent coverage against Pasteurella multocida and polymicrobial flora 2, 9, 3, 8

For penicillin-allergic patients, doxycycline 100 mg twice daily is the preferred alternative 2, 3