Synovial interleukin‐6 point‐of‐care testing, alone and combined with D‐dimer, supports rapid diagnosis of periprosthetic joint infection

Abstract Purpose Data on the reliability of point‐of‐care (POC) tests for the rapid diagnosis of periprosthetic joint infections (PJI) using synovial fluid (SF) D‐dimer (DD), interleukin 6 (IL‐6) and procalcitonin (PCT) are limited. This study aimed to address this issue by evaluating the diagnostic accuracy of POC tests for SF DD, IL‐6 and PCT in comparison to standard laboratory devices for diagnosing PJI. Methods A total of 273 patients who underwent 300 revision arthroplasties were included in this study. According to the European Bone and Joint Infection criteria, 123 were classified as infected, 145 as aseptic revisions and 32 as likely infected. SF DD, IL‐6 and PCT levels were quantified using both POC and standard laboratory tests. The diagnostic accuracy was assessed using receiver operating characteristic curves and area under the curve (AUC). Results Among POC tests, IL‐6 demonstrated the highest AUC 0.83 (95% confidence interval CI 0.77–0.89), followed by DD (0.66, 95% CI 0.59–0.72), while PCT performed poorly (AUC 0.26, 95% CI 0.20–0.33). Laboratory‐based IL‐6 test outperformed all other markers (AUC 0.94, 95% CI 0.90–0.97). When using both POC and standard laboratory methods, significant differences were noted for IL‐6 and DD ( p < 0.001). Combining the POC test results for IL‐6 and DD showed better diagnostic performance than either alone (AUC 0.92). In patients with PJI, biomarker levels differed by pathogen virulence, except for POC IL‐6 ( p = 0.631), POC DD ( p = 0.080) and laboratory DD ( p = 0.053). Conclusions POC tests for SF, particularly those for IL‐6, support the rapid PJI diagnosis, and combining POC IL‑6 with DD further improves diagnostic accuracy. These findings suggest that POC IL‐6, either independently or in conjunction with DD, could be useful in situations where rapid decisions are required. However, its inferior performance compared to that of laboratory assays highlights the need for further optimisation and validation. Level of Evidence Level II, development of diagnostic criteria in a consecutive series of patients and a universally applied ‘gold’ standard.