Predictive value of the usual clinical signs and laboratory tests in the diagnosis of septic arthritis

Objective: To determine the sensitivity and specificity of clinical and laboratory signs for the diagnosis of septic arthritis (SA). Patients and methods: This prospective study included all adult patients with suspected SA seen in the emergency department or rheumatology department at the University Hospital, Clermont-Ferrand, France, over a period of 18 months. Results: In total, 105 patients with suspected SA were included, 38 (36%) presenting with SA (29 [28%] with bacteriologically documented SA). In the univariate analysis, chills (p = 0.015), gradual onset (p = 0.04), local redness (p = 0.01), as well as an entry site for infection (p = 0.01) were most often identified in SA. A history of crystal-induced arthritis (p = 0.004) was more frequent in non-SA cases. An erythrocyte sedimentation rate (ESR) > 50mm (p = 0.005), a C-reactive protein (CRP) level > 100 mg/L (p = 0.019), and radiological signs suggestive of SA (p = 0.001) were more frequent in the SA cases. Synovial fluid appearance: purulent (p < 0.001) and clear (p = 0.007), synovial white blood cell (WBC) count > 50,000/mu L (p < 0.001), differentiated between SA and non-SA. In multivariate analysis, only chills (odds ration [OR] = 4.7, 95% confidence interval [CI] 1.3-17.1), a history of crystal-induced arthritis (OR = 0.09, 95% CI 0.01-0.9), purulent appearance of the joint fluid (OR = 8.4, 95% CI 2.4-28.5), synovial WBC count > 50,000/mm(3) (OR = 6.8, 95% CI 1.3-36), and radiological findings (OR = 7.1, 95% CI 13-37.9) remained significant. Conclusion: No clinical sign or laboratory test (excluding bacteriological test), taken alone, is conclusive for the differentiation between SA and non-SA, but the association of several signs, notably chills, history of crystal-induced arthritis, radiological findings, and the appearance and cellularity of joint fluid may be suggestive.