Sensitivity of erythrocyte sedimentation rate and C-reactive protein for the exclusion of septic arthritis in emergency department patients.

BACKGROUND: Previous studies in post-operative orthopedic and pediatric patients suggest that erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) testing may be helpful in ruling out septic arthritis. However, these tests have not been evaluated in a population of adult Emergency Department (ED) patients.

STUDY OBJECTIVE: Determine the sensitivity of ESR and CRP in patients with septic arthritis.

METHODS: Retrospective analysis of ED patients with septic arthritis from 2003 to 2008. Eligible patients had an International Classification of Diseases-Ninth Revision diagnosis of pyogenic arthritis (711.0x) plus: positive synovial fluid culture, positive synovial Gram stain, or operative irrigation. Patients were excluded if no ESR or CRP was performed within 24 h. Sensitivity of ESR and CRP at various cutoffs was calculated with 95% confidence intervals (CI).

RESULTS: We identified 167 patients with septic arthritis. We included 143 (86%) who had ESR (n=140, 84%) or CRP (n=96, 57%) performed. Mean age was 49 (± 22) years, and 85 (59%) were male. Race was: 125 (87%) white, 4 (3%) black, and 12 (8%) Hispanic. Thirty-five (24%) had infection of prosthetic joints. Synovial cultures were positive in 102 (71%). Sensitivity of ESR was: 98% (95% CI 94-100%) using a cutoff of ≥10 mm/h (n=134) and 94% (95% CI 88-97%) using a cutoff of ≥15 mm/h (n=131). The sensitivity of CRP was 92% (95% CI 84-96%) using a cutoff of ≥20 mg/L (n=88).

CONCLUSION: ESR and CRP have sensitivities of >90% for septic arthritis, but only when low thresholds are used. Further study is required to determine the clinical usefulness of ESR and CRP testing.