Can C-Reactive Protein Be Used to Predict Acute Septic Arthritis in the Adult Population?

OBJECTIVES: The objective of this study was to establish whether C-reactive protein (CRP) could be used to predict native joint septic arthritis (SA) in the adult population. METHODS: All patients who underwent native joint aspiration in accident and emergency settings between April 2012 and September 2016 were identified from laboratory microbiology records. Patients were divided into three groups for analysis: patients with SA, patients with crystal arthropathy, and patients with normal or osteo/inflammatory arthritic joints. RESULTS: Fifteen patients (7.9%) were deemed to have SA, 18 patients had crystal arthropathy (9.5%), and 157 patients (82.6%) were deemed to have normal or osteo/inflammatory arthritic joints. All of the patients with CRP >200 mg/L had SA. Patients with CRP 90 to 200 mg/L had a mix of crystal arthropathy and SA, and patients with CRP <90 mg/L had either normal or osteo/inflammatory arthritic joints or crystal arthropathy. The mean CRP in patients with a normal or osteo/inflammatory arthritic joint was 25 mg/L. This was compared with 100 mg/L (P ≤ 0.001) in patients with crystal arthropathy and 308 mg/L (P ≤ 0.001) in patients with SA. CONCLUSIONS: We demonstrated CRP to be a reliable independent marker to help differentiate among SA, crystal arthropathy, and normal/arthritic joints in an adult population. No patients with CRP <90 mg/L had SA.