Limited Diagnostic Utility of Alpha Defensin in the Diagnosis of Periprosthetic Joint Infection

Abstract Introduction/Objective A key component of laboratory stewardship is appropriate test utilization. We evaluated the utility of alpha defensin (AD), a synovial fluid biomarker, in the diagnosis of periprosthetic joint infection (PJI). Since PJI remains a diagnostic challenge in the orthopedic community, the Musculoskeletal Infection Society (MSIS) created the PJI score, a point-based criteria to help risk stratify the likelihood of infection. The score includes AD, synovial fluid white blood cell count, synovial fluid percent neutrophils, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). AD is a specialized test which adds substantial cost to the evaluation of PJI .The purpose of this study was to investigate the diagnostic utility of the PJI score with AD and without AD (routine laboratory testing of serum and synovial fluid). Methods/Case Report Retrospective chart review was completed on 222 patients with suspected PJI identified at Geisinger Health between January 2019 – March 2021. Data was retrieved through Geisinger’s Phenomic and Analytics Data Core and imported into Excel and JMP v.12 for analysis. All available components of MSIS diagnostic criteria were collected for each patient. Results (if a Case Study enter NA) Of the 222 patients with AD testing, 81% of results were negative (n=178) and 19% results were positive (n=44). AD results corresponded with synovial fluid white blood cell count in 96 % of patients (213/ 222). All components of the PJI diagnostic criteria were collected in 69% of the patients (157/222). Diagnostic criteria calculated without AD showed 43% infected (68/157), 37% possibly infected (58/157), and 20% infected (31/157). Diagnostic criteria calculated with AD showed 43% infected (68/157), 35% possible infected (55/157), and 22% infected (34/157). PJI score including AD compared to PJI score excluding AD showed similar correlation (R2 = 0.93). Conclusion It was found that AD testing does not provide substantial diagnostic value in the evaluation of PJI. Synovial fluid cell count was found to directly correlate with alpha defensin suggesting it’s potential use as a surrogate marker for clinical decision making. Diagnostic criteria obtained through routine testing of serum (ESR, CRP) and synovial fluid (WBC, percent neutrophils) provides sufficient data for diagnosis.