The gap between practice and methodology: the case of esterase in Periprosthetic Joint Infection

Introduction: the diagnosis of periprosthetic joint infection (PJI) is a clinical challenge. Among other clinical and laboratory parameters, recent recommendations for the diagnosis of PJI advocate the assessment of leukocyte esterase in synovial fluid (SF), commonly performed with urine test strips, a method that is not validated for such a matrix. To challenge this practice, we evaluated the performance of a commercial urine test strip to assess leukocyte esterase in SF compared with leukocyte counting. Methods: between October 2017 and September 2019, SF samples were collected from patients scheduled for revision surgery for 6 painful total knee arthroplasties. International Consensus Meeting (ICM) criteria were used to classify PJI. Leukocyte esterase (visual assessment with Menarini Aution test strips) and automated leukocyte count (Sysmex 2000, XN- 8 Body Fluids Module) were assessed in 74 SF specimens. Results: the AUC of leukocyte esterase compared with automated leukocyte counting ranged from 0.88 to 0.94. Leukocyte esterase cutoff values of 500, 250, and 75 leukocytes/µL yielded sensitivity values ranging from 0.78-1.00, 0.87-1.00, and >0.96, respectively, whereas specificity ranged from 0.76-0.94, 0.61-0.78, and <0.37. The diagnostic performance of leukocyte esterase was higher when hemolyzed samples were excluded. Discussion: our results highlight the many limitations of using conventional urine test strips to visually assess leukocyte esterase in SF specimens, underscoring the need to develop specific assays or perform validation studies before implementing a diagnostic procedure.