Recent Antibiotic Treatment Impacts Serum and Synovial Laboratory Values in Early Periprosthetic Joint Infection Workup.

Background: Accurately detecting early postoperative periprosthetic joint infection (PJI) following total hip arthroplasty (THA) and total knee arthroplasty (TKA) remains challenging. The purpose of our study was to determine the impact of antibiotics given prior to laboratory evaluation on the reliability of serologic and synovial fluid tests to identify PJI in the early postoperative period.
Methods: We identified 49,861 primary total hip arthroplasties and total knee arthroplasties performed between 2000 and 2019. Among these patients, 21 hips and 28 knees that underwent arthrocentesis within 12 weeks of their arthroplasty were identified as infected. Patients who had received antibiotics within 2 weeks prior to laboratory evaluation were compared to those who had not. Median values of C-reactive protein, erythrocyte sedimentation rate, synovial white blood cell (WBC) count, synovial neutrophil percentage, and synovial absolute neutrophil count were compared between groups. The false negative rate for detecting PJI using laboratory values was compared using published cutoffs for PJI in the early postoperative period.
Results: Median values of C-reactive protein (105 vs 22 mg/L; P = .006), synovial WBC count (57,591 vs 4,473 cells/μL; P = .003), synovial neutrophil percentage (94% vs 76%; P = .004), and synovial absolute neutrophil count (50,748 vs 2,804 cells/μL; P < .001) were significantly lower in patients who received antibiotics compared to those who did not. False negative rates for detecting PJI were significantly higher for synovial WBC and synovial neutrophil percentage in patients treated with antibiotics compared to untreated patients.
Conclusion: False negative rates for detecting early PJI when using published cutoffs were markedly higher in antibiotic-treated patients compared to untreated patients for synovial WBC count and synovial neutrophil percentage.
Level of Evidence: Level IV retrospective review.
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