Alpha-Defensin and Synovial Proteins to Improve Detection of Pediatric Septic Arthritis

The purpose of this study is to determine if alpha-defensin and other proteins present in joint fluid may be able to rapidly diagnose bacterial joint infections. Patients with suspected joint infection typically undergo joint aspiration so that tests can be performed to help diagnose joint infection, including gram stain, cell count, and culture. Patients under 18 years old that are undergoing sampling of their joint fluid due to suspicion of infection or inflammation will be enrolled in this multi-center trial. Joint fluid will also be sampled from normative controls made up of patients who are undergoing an unrelated procedure without inflammation or infection. Joint fluid from patients with suspected inflammation/infection and from normative controls will be analysed for presence of alpha-defensin, leukocyte esterase, neutrophil elastase, synovial C-reactive protein, and synovial lactate. The alpha-defensin assay has shown high sensitivity and specificity for joint infection in other studies. Additionally a Staphylococcus spp antigen panel, Candida spp antigen panel, Enterococcus faecalis assay, BACTAlert culture, cell count plus differential, gram stain, and aerobic, anaerobic, and fungal cultures will be done using synovial fluid. A synovial fluid PCR for Kingella kingae will be performed if the patient is under eight years of age. Blood tests will include cell count and differential, erythrocyte sedimentation rate, C-reactive protein, procalcitonin, and D-dimer, as well as relevant inflammatory or rheumatologic marker tests. Results from these tests will be compared to joint fluid culture which the gold standard for diagnosing bacterial infection. The study includes 1 visit per patient, the standard of care visit in which the patient would be undergoing joint aspiration or arthroscopy. Once data has been collected, the sensitivity and specificity will be determined for these experimental tests both individually and in combination.