Leukocyte esterase strip test may reliably diagnose infection persistence
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Use of a leukocyte esterase strip test may be a reliable tool to diagnose persistence of infection during second-stage revision procedures for periprosthetic joint infection, according to results.
Researchers collected synovial fluid for leukocyte esterase measurement among 76 patients who underwent a two-stage exchange for periprosthetic joint infection between July 2015 and April 2020. The synovial fluid collection occurred during surgery before arthrotomy in 79 procedures, according to researchers. Researchers generated receiver operating characteristic curves and calculated sensitivity, specificity, positive predictive value, negative predictive value, accuracy and area under the curve of leukocyte esterase, C-reactive protein, erythrocyte sedimentation rate (ESR) and the combination of serum CRP and ESR.
Results showed the leukocyte esterase assay had a sensitivity of 82%, specificity of 99%, positive predictive value of 90% and negative predictive value of 97%. The leukocyte esterase test had a threshold of 1.5 between the first (negative) and second (positive) level of ordinal variable, according to receiver operating characteristic analysis. Researchers noted diagnosis of persistent infection was accurate with a grade starting from 1 plus. Researchers found a threshold of 8.25 mg/L and 45 mm/h were the best thresholds for the CRP assay and ESR assay, respectively.
“Given its simplicity, speed and relatively low cost, the [leukocyte esterase] test may be advantageously used to determine infection persistence at reimplantation in staged revisions in combination with other [Musculoskeletal Infection Society] criteria,” the authors wrote.
Perspective
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The authors finding that ESR and CRP can be misleading at the time of reimplantation is spot-on and confirms previous work in the field. Their finding on the leukocyte esterase test strip at the time of revision is worth considering and highlights the ongoing struggle that surgeons face in making decisions at the time of reimplantation – no tests are perfect. The authors are refreshingly honest and clear in pointing out that studies on reimplantation diagnostics are inherently limited by a lack of gold standard, low infection prevalence and difficulty in quantifying outcomes.
For these reasons and others, I would hesitate to recommend the widespread use of leukocyte esterase test strips at the time of reimplantation given the potential for errors. First, proper off-label use of the leukocyte esterase test strip for synovial fluid requires a sophisticated understanding of diagnostics, including an appreciation of the subtlety that the leukocyte esterase cutoff used in this reimplantation study (+1 cutoff) is different than that in the Musculoskeletal Infection Society and International Consensus Meeting criteria (+2 cutoff). Second, the proper off-label use of the leukocyte esterase test strip requires substantial institutional standardization efforts as accomplished in this study, including the involvement of laboratory methods (centrifugation) and staff (senior biologist). Although the leukocyte esterase test strip is fast and cheap, I believe that its off-label use should be restricted to major arthroplasty centers with the appropriate infrastructure and expertise.
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