SUMMARY
This study aimed to test the accuracy of the synovial fluid biomarker, a-defensin, in diagnosing septic arthritis in native joints and highlight the pitfalls of its utilization for primary joints. We also discuss the cases where false results were demonstrated.A retrospective review of 10 patient’s records, who underwent a-defensin testing for suspected primary joint infections prior to performing arthroplasty surgery, was performed.6 primary knee and 4 primary hip joints were evaluated for septic arthritis utilizing the a-defensin test after arthrotomy was performed, as the patient had turbid synovial fluid or atypical bony features suggestive of septic arthritis. 2 of the primary hip joints had previous cephalomedullary nail insertions that cut-out and 1 knee joint had previous distal femur fixation for peri-articular fracture. There were 2 false positive a-defensin results in native knee joints that were eventually attributed to inflammatory arthritis after extensive cultures and microbial sequencing results returned negative. All other patients had negative a-defensin results that correlated with anti-microbial testing.The utilisation of the a-defensin test in primary joints should be interpreted with caution. The elevated levels of a-defensin may be attributable to inflammatory arthritis and further studies of its levels in native joints are required.