How Reliable Is the Cell Count Analysis in the Diagnosis of Prosthetic Joint Infection?

Synovial analysis of joint aspirates is a key diagnostic tool; all major diagnostic algorithms include cell count (CC) and polymorphonuclear percentage (PMN%) as important criteria to make the diagnosis. In this context, we conducted this study to analyze the overall accuracy of CC and PMN%.

A single-center retrospective analysis was performed with clinical data of included patients, with a total of 524 preoperative joint aspirations (255 hips, 269 knees). From the aspirated synovial fluid, we tested the leukocyte esterase activity, leukocyte CC, and PMN%, and sent specimens for aerobic and anaerobic bacterial culture. Depending on the clinical results in accordance with the Musculoskeletal Infection Society criteria for prosthetic joint infection (PJI), 203 patients were then admitted for aseptic revision and 134 patients for septic exchange.

In 337 cases (64.3% of the study patients), it was possible to measure the CC. The best cutoff level for PJI of all study patients was 2582 leukocytes/μL (sensitivity [SE] 80.6%, specificity [SP] 85.2%) and a PMN% of 66.1% (SE 80.6%, SP 83.3%). The chosen cutoff levels for PJI of total knee and total hip arthroplasty were 1630 leukocytes/μL (SE 83.6%, SP 82.2%) and a PMN% of 60.5% (SE 80.3%, SP 77.1%) and 3063 leukocytes/μL (SE 78.1%, SP 80.0%) and a PMN% of 66.1% (SE 82.2%, SP 82.4%), respectively.

CC and PMN% are sensitive methods for diagnosing PJI of total hip and total knee arthroplasty. However, there are differences in cutoff levels between knees and hips. International guidelines and diagnostic criteria need revisions in terms of these parameters.