Accuracy of the α-defensin lateral flow assay for diagnosing periprosthetic joint infection in Asians

Objective: This study aimed to test the accuracy of the Synovasure®, α-defensin lateral flow test kit, in diagnosing periprosthetic joint infections (PJIs) in a predominantly Asian population and to evaluate whether other patient or disease factors may affect its results. Methods: 61 Asian patients comprising 70 hip or knee prosthetic joints, performed between November 2015 and November 2018, were retrospectively evaluated. Cases were categorized as infected or not infected using Musculoskeletal Infection Society (MSIS) Criteria. Synovial fluid was tested for α-defensin using a commercially available kit. . Results: The Synovasure test had a sensitivity of 73.7% (95% confidence interval (CI): 48.8–90.9%) and specificity of 92.2% (95% CI: 81.1–97.8%) in an Asian population, which was slightly lower compared to previously reported studies in a predominantly Caucasian population. The positive predictive value was 77.8% (95% CI: 56.8–90.3%) and the negative predictive value was 90.4% (95% CI: 81.5–95.2%). The test had an area under curve (AUC) of the receiver operating characteristic (ROC) graph of 0.938, which represents an accuracy that is similar to synovial white blood cells (WBCs) and almost equivalent to that of synovial polymorphonuclear cells (PMNs). The presence of diabetes (p = 0.26), systemic inflammatory joint disease (p = 0.33), other metallic implants (p = 0.53), immunosuppression (p = 0.13), prior antibiotic usage (p = 0.99), and chronicity of symptoms (p = 0.34) was not significantly associated with a positive test in patients with PJI. Conclusion: The α-defensin lateral flow test kit is highly accurate in the diagnosis of PJI but with slightly lower sensitivity and specificity in an Asian population when compared with previous studies. The test should be used in conjunction with other MSIS criteria to provide clinically relevant and meaningful results for the diagnosis of PJI.