Detection of α–defensin in synovial fluids by MALDI‐ToF mass spectrometry as innovative and cost effective assay for improved definition of periprosthetic joint infections

RATIONALE: alpha-Defensins detection in synovial fluid is gaining more and more interest in the field of correct diagnosis of periprosthetic joint infections (PJIs). At present, they can be assessed by a quantitative enzyme-linked immunosorbent assay which is expensive and time-consuming and by a qualitative lateral flow immunoassay which is rapid but quite expensive and whose clinical sensitivity is debated. Thus, developing an alternative rapid, accurate, and low-cost alpha-Defensins assay is important to make alpha-Defensins actionable as novel key clinical marker. METHODS: Eighteen synovial fluid (SF) samples were obtained from 18 patients undergoing revision of primary joint arthroplasty. Of these, 8 met the 2013 Musculoskeletal Infection Society (MSIS) criteria for PJIs, the remaining were classified as aseptic failure. Microbiological analysis and Synovasure were carried out on all samples. Sample preparation and the MALDI-ToF mass spectrometry setting were adjusted to detect Human Neutrophil Peptide (HNP)-1, -2 and -3 and to obtain optimal results in term of sensitivity and stability. RESULTS: MALDI-ToF MS was able to detect HNPs in SF from septic patients. No HNPs signals were detected in SF from aseptic failure. The limit of detection was 2.5 and 1.25 mug/ml for HNP-2 and HNP-1, respectively. The turnaround time of the analysis is 20 minutes, and SF samples are stable at -20 degrees C for up to 3 days. Assay sensitivity, specificity, and positive and negative predictive values (PPV and NPV) were 100% for all parameters. On the same SF samples, the Synovasure assay showed lower sensitivity, specificity, PPV and NPV of 87.5%, 90%, 87.5% and 90%, respectively. Microbiological analysis of SF confirmed the presence of bacteria only in SF MSIS-positive patients. CONCLUSIONS: The reported MALDI-ToF assay was able to detect and differentiate HNPs in SF samples and showed a slightly better diagnostic accuracy than the Synovasure assay.