Abstract
Aim
Alpha-defensin is a new synovial fluid biomarker for the diagnosis of periprosthetic joint infections (PJI). We compared the performance of two different alpha-defensin assays: quantitative ELISA test and qualitative lateral flow test.
Method
In this prospective cohort study, consecutive patients with a painful prosthesis of the lower limb were eligible for inclusion. In addition to standard diagnostics of PJI, alpha-defensin was determined in the aspirated synovial fluid between October 2016 and April 2017. PJI was defined according to the modified Zimmerli criteria, the Musculoskeletal Infection Society (MSIS) criteria and the Infectious Disease Society of America (IDSA) criteria. A positive quantitative alpha-defensin test was defined at a cut-off value of 5.2 mg/L. The sensitivity, specificity, accuracy and area under the curve of each test were determined and the AUCs were compared among each other.
Results
We included 72 patients (55 knee, 27 hip prosthesis) with a median age of 70 years (range: 41 – 85 years). Based on the modified Zimmerli criteria, 23 cases (32%) were categorized as septic and 49 (68%) as aseptic prosthesis failure. The sensitivity, specificity, accuracy, and AUC of quantitative alpha-Defensin were 48%, 98%, 82%, and 0.73, respectively; for qualitative alpha-Defensin, results were 48%, 100%, 83%, and 0.74, respectively. When the IDSA criteria were applied, the sensitivity of the quantitative and qualitative alpha-defensin test was 83% and 75%, respectively; when the MSIS criteria were applied, the sensitivity of the quantitative and qualitative alpha-Defensin was 92% and 83%, respectively. The comparison between the qualitative and quantitative alpha-defensin tests showed no statistically significant difference regardless of the used infection classification (modified Zimmerli: [difference AUC −0.01; p = 0.792], IDSA: [difference AUC 0.04; p = 0.317], MSIS: [difference AUC 0.04; p = 0.264]).
Conclusions
The sensitivity of the alpha-defensin test in synovial fluid showed poor sensitivity (48%) for diagnosing PJI when modified Zimmerli criteria were used. No difference were observed between the qualitative and quantitative alpha-defensin test.
