Septic Arthritis - Native Joint
Initial Investigations

Initial Investigations

Testing

Presentation: Joint pain, swelling, decreased ROM; most are febrile, but older patients may be afebrile

  • Should be obtained in all patients
  • To assess for fluid if findings unclear
  • Cell count & differential (in EDTA tube)
  • Gram stain & culture
  • Crystal analysis (re: gout)
  • Molecular testing for pathogens available if cultures negative (consult ID)
  • C-reactive protein (CRP)
  • Elevation can be delayed
  • Valuable to monitor treatment response over time
  • Lyme Disease
  • Hepatitis B
  • Rubella
  • Parvovirus B19
  • Chikungunya (travel history)
  • ASOT (for post-Streptococcal arthritis & acute rheumatic fever)
  • Brucella

Interpreting Synovial Fluid Results

WBC > 25,000 supports infection

WBC > 50,000 has increased specificity