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Guidelines
Interpreting Lab Results

Interpreting Lab Results

Patients with synovial fluid crystals may still have concomitant septic arthritis.

Progressively higher synovial WBC count increases the likelihood ratio (LR) of septic arthritis:

  • Synovial WBC count > 50 X109/L has a positive LR of 7.7 for septic arthritis
  • Synovial WBC count >100 X109/L has a positive LR of 28.0 for septic arthritis
  • PMN cell count of >90% has a positive LR of 3.4 for septic arthritis