The diagnostic value of platelet-related indicators to CRP ratio in periprosthetic joint infection.

OBJECTIVE: To evaluate the diagnostic value of platelet-to-CRP ratios for periprosthetic joint infection (PJI) following total joint arthroplasty, and to assess the influence of potential confounders. METHODS: A retrospective case-control study included 151 PJI patients and 178 with aseptic loosening (AL). CRP, ESR, PLT, PDW, PLT/CRP, PLT/ESR, and PDW/CRP were compared between groups. ROC curves assessed diagnostic performance. Subgroup analyses stratified by joint (hip/knee) and infection duration (acute/chronic) were performed. Multivariate regression adjusted for time-related covariates, with pairwise ROC comparisons via DeLong test. RESULTS: Joint distribution, symptom duration, diabetes, and time from arthroplasty differed significantly between groups (all P < 0.05); sex, age, laterality, revision history, and immunosuppression did not. All seven biomarkers differed significantly between PJI and AL groups (all P < 0.0001). PDW/CRP achieved the highest AUC (0.9047), with 84.3% sensitivity and 84.8% specificity, followed by CRP (AUC = 0.9002) and PLT/CRP (AUC = 0.8841). Single platelet markers performed poorly (AUCs < 0.66). No significant joint-specific differences were observed (all P > 0.05). PDW/CRP showed higher AUC in acute (0.9452) versus chronic PJI (0.8901, P = 0.0407). All seven biomarkers remained significantly associated with PJI after adjustment for time-related variables (all P < 0.01). DeLong tests confirmed that PLT/CRP and PDW/CRP were comparable to CRP alone (both P > 0.05), while significantly outperforming single platelet parameters (all P < 0.001). CONCLUSION: PLT/CRP and PDW/CRP are low-cost adjunctive biomarkers for PJI diagnosis, with PDW/CRP offering well-balanced sensitivity and specificity. Their diagnostic performance is stable across hip and knee joints and independent of symptom duration or implantation time. External validation in unselected populations is warranted.