Traditional Laboratory Markers Hold Low Diagnostic Utility for Immunosuppressed Patients With Periprosthetic Joint Infections

Although predictive laboratory markers and cutoffs for immunocompetent patients are well-studied, similar reference ranges and decision thresholds for immunosuppressed patients are less understood. We investigated the utility of typical laboratory markers in immunosuppressed patients undergoing aspiration of a prosthetic hip or knee joint.

A retrospective review of adult patients with an immunosuppressed state that underwent primary and revision total joint arthroplasty with a subsequent infection at our tertiary, academic institution was conducted. Infection was defined by Musculoskeletal Infection Society criteria. A multivariable analysis was used to identify independent factors associated with acute (<90 days) and chronic (>90 days) infection. Area under the receiver-operator curve (AUC) was used to determine the best supported laboratory cut points for identifying infection.

We identified 90 patients with immunosuppression states totaling 172 aspirations. Mean follow-up from aspiration was 33 months. In a multivariate analysis, only synovial fluid cell count and synovial percent neutrophils were found to be independently correlated with both acute and chronic infection. A synovial fluid cell count cutoff value of 5679 nucleated cells/mm ³ maximized the AUC (0.839) for predicting acute infection, while a synovial fluid cell count cutoff value of 1293 nucleated cells/mm ³ maximized the AUC (0.931) for predicting chronic infection.

Physicians should be aware of lower levels of synovial nucleated cell count and percentage of neutrophils in prosthetic joint infections of the hip or knee in patients with immunosuppression. Further investigation is necessary to identify the best means of diagnosing periprosthetic joint infection in this patient population.