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Leukocyte Esterase Reagent Strips Help Diagnose PJI

Award-winning study finds strips are effective for rapid diagnosis of infection

Jennie McKee

Leukocyte esterase reagent (LER) strips, commonly used for diagnosing conditions such as urinary tract infections, peritonitis, and chorioamnionitis, may also be helpful in rapid diagnosis of periprosthetic joint infection (PJI), according to a paper presented at the 2011 annual meeting of the American Association of Hip and Knee Surgeons that received the James A. Rand Award.

The prospective study built on previous work conducted by Javad Parvizi, MD, FRCS, and fellow researchers that suggested LER strips could potentially play a role in rapid diagnosis of PJI.

Testing with LER strips
The study included 223 patients who had a suspected PJI after undergoing total joint arthroplasty (180 total knee arthroplasties and 43 total hip arthroplasties). Testing was done either in the office (156 patients) or in the operating room (67 patients).

Researchers considered the LER strip positive for infection only if the number of white blood cells (WBC) was measured as “moderate” or “large,” (or + or ++, depending on the manufacturer of the strip). Trace and small leukocyte results were considered to be negative for infection. The researchers compared the LER results with cultures and correlated them with the synovial fluid WBC.

Analyzing the results
Researchers reported that 52 strips were read as positive, while 106 had negative results and 65 strips could not be read due to debris of blood or metal in the aspiration. A synovial fluid WBC of more than 3,000 WBC/uL served as the comparative standard (the cutoff used at the author’s institution for diagnosing PJI). Based on these criteria, the LER strips had a sensitivity of 92.9 percent and a specificity of 88.8 percent. When researchers used positive cultures or the presence of a draining sinus tract as the gold standard, however, the sensitivity and specificity values of the LER strips were 93.3 percent and 77 percent, respectively.

LER strip sensitivity was 100 percent and specificity was 86.8 percent in the 67 reoperations.

Drawing conclusions
In summary, noted the researchers, “LER strips represent a rapid, inexpensive, and sensitive tool for the diagnosis of PJI that seems to correlate well with the synovial fluid WBC count.”

They cautioned, however, that the strips’ utility can be limited by “blood or debris in the synovial fluid, rendering them unreadable in nearly one-third of cases.”

Mr. Wetters reported no conflicts of interest. His coauthors for “Leukocyte esterase reagent strips for the rapid diagnosis of periprosthetic joint infection” included Keith R. Berend, MD (Biomet and Salient Surgical Technologies); Adolph V. Lombardi, Jr, MD, FACS (Biomet, Innomed, Stryker, Salient Surgical Technologies, and Angiotech); Michael J. Morris, MD (Biomet); Tawnya L. Tucker (no conflicts), and Craig J. Della Valle, MD (Biomet, Convatec, CD Diagnostics, Smith & Nephew, and Stryker).

Download the final program and read the abstract: http://www.aahks.org/meetings/anmeet/pastanmeets/AM11FinalProgram.pdf (page 17)

AAOS Now
January 2012 Issue
http://www.aaos.org/news/aaosnow/jan12/clinical2.asp