Laboratory Value Effectiveness in Predicting Early Postoperative Periprosthetic Joint Infection After Total Hip Arthroplasty

Background: Diagnosing early periprosthetic joint infection (PJI) after primary total hip arthroplasty (THA) remains challenging. We sought to validate optimal laboratory value cutoffs for detecting early PJIs in a series of primary THAs from one institution. Methods: We retrospectively identified 22,795 primary THAs performed between 2000 and 2019. Within 12 weeks, 43 hips (43 patients) underwent arthrocentesis. Patients were divided into 2 groups: evaluation ≤6 weeks or 6-12 weeks following THA. The 2011 Musculoskeletal Infection Society major criteria for PJI diagnosed PJI in 15 patients. Mann-Whitney U-tests were used to compare median laboratory values and receiver operating characteristic curve analysis was used to evaluate optimal cutoff values. Results: Both within 6 weeks and between 6 and 12 weeks postoperatively, median C-reactive protein (CRP), erythrocyte sedimentation rate, synovial white blood cell (WBC) count, neutrophil percentage, and absolute neutrophil count (ANC) values were significantly higher in infected THAs. Optimal cutoffs within 6 weeks were: CRP ≥100 mg/L, synovial WBCs ≥4390 cells/μL, neutrophil percentage ≥74%, and ANC ≥3249 cells/μL. Between 6 and 12 weeks, optimal cutoffs were: CRP ≥33 mg/L, synovial WBCs ≥26,995 cells/μL, neutrophil percentage ≥93%, and ANC ≥25,645 cells/μL. Conclusion: Early PJI following THA should be suspected within 6 weeks with CRP ≥100 mg/L or synovial WBCs ≥4390 cells/μL. Between 6 and 12 weeks postoperatively, cutoffs of CRP ≥33 mg/L, synovial fluid WBC ≥26,995 cells/μL, and neutrophil percentage ≥93% diagnosed PJI with high accuracy. Level of Evidence: Level IV Diagnostic.