Serum Interleukin-6 Exhibits Better Diagnostic Performance Than Serum C-Reactive Protein in Acute Periprosthetic Joint Infection.

Background: Inflammatory biomarkers serve as the first-line screening tools for diagnosing periprosthetic joint infection (PJI). However, the kinetics and trajectory of each biomarker in response to inflammatory stimuli vary. This study aimed to identify the most reliable diagnostic predictors for acute and chronic PJI through a comprehensive evaluation of the diagnostic accuracy of commonly utilized serum biomarkers.

Methods: We retrospectively analyzed 282 patients undergoing revision total hip or knee arthroplasty between January 2016 and October 2022. After exclusions, 218 patients were categorized into acute PJI (n = 46), chronic PJI (n = 62), and non-PJI (n = 110) groups. A PJI diagnosis was established according to the 2013 International Consensus Meeting (ICM) criteria. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic value of serum biomarkers, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), interleukin-6 (IL-6), plasma fibrinogen (FIB), and platelet count (PLT).

Results: The IL-6 demonstrated the highest diagnostic accuracy for acute PJI, with an area under the curve (AUC) of 0.929, followed by CRP (0.853), ESR (0.816), FIB (0.788), and PLT (0.683). In contrast, CRP showed the highest diagnostic accuracy for chronic PJI, with an AUC of 0.908, followed by IL-6 (0.899), FIB (0.883), ESR (0.850), and PLT (0.770). For acute PJI diagnosis, the optimal cutoff value for IL-6 was determined to be 7.2 pg/mL, demonstrating a sensitivity of 93.5%, specificity of 83.6%, positive predictive value (PPV) of 70.5%, and negative predictive value (NPV) of 96.8%. For chronic PJI diagnosis, the optimal cutoff value for CRP was 15.1 mg/L, yielding a sensitivity of 77.4%, specificity of 91.8%, PPV of 84.2%, and NPV of 87.8%.

Conclusions: Serum IL-6 and CRP exhibit excellent diagnostic performance for acute and chronic PJI, respectively. Pairing comparison reveals that IL-6 represents the most accurate biomarker for diagnosing acute PJI.