Diagnosis of periprosthetic joint infection: the threshold for serological markers.

BACKGROUND: Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) have recently been suggested as diagnostic criteria for periprosthetic joint infection (PJI) diagnosis. Thresholds for these markers should be reexamined since they have been determined arbitrarily. QUESTIONS/PURPOSES: Based on recently defined criteria for PJI, we determined (1) whether there is a difference in the threshold value of ESR and CRP between hips and knees, (2) whether the threshold value for ESR and CRP should be different for early-postoperative and late-chronic PJI, and (3) the optimal thresholds for ESR and CRP in PJI diagnosis.
METHODS: We retrospectively reviewed 1962 patients with revision arthroplasty for aseptic failure (1095 hips, 594 knees) or first onset of PJI (108 hips, 165 knees) between 2000 and 2009. The PJI diagnosis was made independent of ESR and CRP using criteria recently proposed by the Musculoskeletal Infection Society. Patients with comorbidities that confound ESR and CRP were not included. Receiver operating characteristic (ROC) analysis was performed to determine thresholds.
RESULTS: ESR and CRP levels in late-chronic PJI were higher in knees than in hips. Optimal thresholds for ESR and CRP were 48.5 mm/hour and 13.5 mg/L in hips and 46.5 mm/hour and 23.5 mg/L in knees, respectively. In early-postoperative PJI, ESR and CRP were similar in both joints with common thresholds of 54.5 mm/hour and 23.5 mg/L, respectively.
CONCLUSIONS: The data suggest a similar threshold for ESR but not for CRP should be implemented for late-chronic hips and knees. Optimal magnitudes are higher than conventional thresholds, indicating the need for refinement of thresholds if ESR and CRP are to be criteria for PJI diagnosis. Early-postoperative and late-chronic PJI might require different thresholds. LEVEL OF EVIDENCE: Level III, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.