Clinical Evaluation of Alpha Defensin Test Following Staged Treatment of Prosthetic Joint Infections

Diagnosing persistent infection following staged treatment of prosthetic joint infection (PJI) is challenging. The alpha defensin (AD) test has been shown to be an accurate diagnostic test for the primary diagnosis PJI but has limited evaluation for use following a staged treatment of PJI. The goal of this study was to evaluate the diagnostic accuracy of AD testing following staged treatment of PJI before reimplantation surgery and to determine if negative AD test predicted success following reimplantation using Delphi Criteria at time of last follow-up.

Patients who underwent AD testing prior to reimplantation after staged treatment of PJI (n = 52) were reviewed. Preoperative data (AD result, synovial fluid [SF], C-reactive protein level [mg/L], SF culture, SF white blood cell count, % of polymorphonuclear lymphocytes, serum C-reactive protein/erythrocyte sedimentation rate) and intraoperative data (purulence and tissue culture) were reviewed and used to classify patients using 2018 Musculoskeletal Infectious Disease Society criteria for infection, which was then used as a gold standard test to calculate diagnostic accuracy.

Chart review was used to determine if patients who underwent reimplantation surgery would go on to treatment failure as defined by Delphi Criteria.

The sensitivity and specificity of AD test result as compared with Musculoskeletal Infectious Disease Society criteria in diagnosing PJI was calculated to be 71% and 97.78%. Positive predictive value was calculated to be 83.3%, and negative predictive value was calculated to be 95.65%.

Patients who underwent reimplantation (46/52 patients) all had negative AD test results, and 9/46 or 19.5% would have treatment failure as defined by the Delphi Criteria with an average follow-up of 588 days.

AD demonstrates high specificity and negative predictive value, with low sensitivity when utilized after staged treatment of PJI. Further investigation of this and other diagnostic tests following staged treatment of PJI is needed. Additionally, validated criteria used to identify persistent infection following staged treatment of PJI are required.