Tag Archive | CRP

Diagnosing PJI: When The “Urine Dipstick” Outperforms Conventional Labs

Despite what seems like a new, high-quality study being published on the topic every week or so, orthopaedic surgeons still have an extremely hard time determining whether a prosthetic hip or knee is infected or not. We have an array of available tests and the relatively easy-to-follow criteria for a periprosthetic joint infection (PJI) from the Musculoskeletal Infection Society (MSIS), but a large number of these patients still fall into the gray zone of “possibly infected.” This predicament is especially thorny in patients who received antibiotics just prior to the diagnostic workup, which interferes with the accuracy of many tests for PJI.

In the April 17, 2019 issue of The Journal, Shahi et al. remind orthopaedic surgeons about a valuable tool that can be used in this scenario. Their retrospective study looked at 121 patients who had undergone revision hip or knee arthroplasty due to an MSIS criteria-confirmed periprosthetic infection. Shahi et al. sought to determine which diagnostic tests were least affected by prior antibiotic administration. The authors found that erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, synovial white blood cell (WBC) count, and polymorphonuclear neutrophil (PMN) percentage were all significantly lower in the 32% of patients who had received antibiotics within 2 weeks of those tests, compared with the 68% who did not receive antibiotics. The only test that was found not to be significantly affected by the prior admission of antibiotics was the urine-based leukocyte esterase strip test.

Considering the ease and rapidity with which a leukocyte esterase test can be performed and evaluated (at a patient’s bedside, with immediate results), its low cost, and the fact that it is included in the MSIS criteria, these findings are very important and useful. While we would prefer that patients with a possibly infected total hip or knee not receive antibiotics prior to their diagnostic workup, previous antibiotic exposure remains a relatively common scenario. The findings from this study can assist us in those difficult cases, and they add further evidence to support the value and reliability of the easy-to-perform leukocyte esterase test.

Chad A. Krueger, MD
JBJS Deputy Editor for Social Media

D-Dimer Levels May Help with PJI Diagnoses

D-dimer for OBuzzThe percentage of periprosthetic joint infections (PJIs) among patients requiring revision arthroplasty of the hip and knee is increasing. PJIs have important clinical implications both for revision surgical procedures as well as pre- and postoperative management. Any extra help we can get making a PJI diagnosis outside of the obvious (where the patient presents with a draining wound) would be most welcome.

In the September 6, 2017 issue of The Journal, Shahi et al. present compelling data from a prospective study suggesting that serum D-dimer levels may help diagnose PJI—and thereby help determine the optimal timing of component reimplantation. The authors determined that 850 ng/mL was the optimal threshold value for D-dimer in diagnosing PJI. Moreover, with sensitivity of 89% and specificity of 93%, this test outperformed the widely used ESR and CRP tests, which until now have proven to be the “best” tools we have at our disposal.

Ideally, after these results are confirmed in larger populations of patients undergoing revision arthroplasty, the serum D-dimer test—inexpensive and almost universally available—will be used in all high-volume joint replacement centers. The continued pursuit of diagnostic and treatment methodologies for patients with suspected PJI is definitely warranted, given the increasing number of patients requiring arthroplasty and combined lifetime knee- and hip-replacement revision rates hovering around 10% to 12%. The identification of D-Dimer elevation as a potentially more accurate diagnostic tool than our currently available tests is a welcome contribution.

Marc Swiontkowski, MD
JBJS Editor-in-Chief