Commercial Synovial Antibody Testing is No Better Than Traditional Culture in Identification of Pathogen(s) Causing Periprosthetic Joint Infection

Background: Identification of infective organism causing periprosthetic joint infections (PJIs) is crucial to tailor the best combination of surgical and antimicrobial treatment. Traditional culture, with all its limitations, has been utilized for this purpose. A synovial fluid antibody assay against some common pathogens has been introduced by a commercial entity recently. This study aimed to determine if the antibody testing could be used as a proxy to traditional culture, and whether it provided additional information, in the setting of PJI. Methods: A retrospective study was conducted of patients who underwent revision total hip and knee arthroplasty between January 2019 and 2020. Aspirated synovial fluid was sent for analyses including the commercial antibody testing. All patients had samples harvested for culture per standard of care. Results of the antibody testing and culture, in terms of concordance, were compared. Receiver operating characteristic curve and Youden's criterion were used to compare the 2 methods. Results: A total of 419 patients were included. Using the International Consensus Meeting criteria as reference standard for PJI, antibody testing had a sensitivity and specificity of 40.5% and 93.4%, respectively. There were 59.5% false negative results with antibody testing compared with 50% for culture. Of the 12 patients who had positive results in both tests, 5 (41.7%) had discordant pathogens identified in each test. Conclusion: Synovial fluid antibody testing does not provide clinical benefit when compared to traditional cultures for PJI diagnosis. The antibody testing had a low sensitivity and a high rate of discordance with culture, when both tests were positive.