What Is the Diagnostic Accuracy of Alpha-Defensin and Leukocyte Esterase Test in Periprosthetic Shoulder Infection?
Authors: Unter Ecker Niklas , Koniker Alina , Gehrke Thorsten , Salber Jochen , Zahar Akos , Hentschke Moritz , Citak Mustafa 
Published: April 2019

Abstract

Background
The diagnosis of periprosthetic joint infection (PJI) after total shoulder arthroplasty (TSA) is challenging, especially in patients with Cutibacterium (formerly Propionibacterium) acnes infection. Despite the increasing number of patients with PJI of the shoulder, there are still no robust data regarding diagnostic tests in detecting shoulder PJI.

Questions/purposes
(1) What are the sensitivity, specificity, and negative- and positive-predictive values for the alpha-defensin enzyme-linked immunosorbent assay test in detecting PJI after TSA? (2) What are the diagnostic accuracies in detecting shoulder PJI for synovial alpha-defensin, leukocyte esterase Test, and serum C-reactive protein (CRP)?

Methods
All patients with painful TSA, who underwent joint aspiration to validate or exclude a PJI, between July 2015 and February 2018 were enrolled in this single-center study. Further indications for aspiration were as follows: planned revision arthroplasty, early loosening and clinical signs of infections, especially serum CRP elevation. A total of 121 patients were aspirated to exclude or verify a PJI, and 16 patients were excluded. In all, 105 patients with a mean age of 68 years (± 12 years) were included for analysis. Patients who underwent TSA were considered aseptic or septic according to the Musculoskeletal Infection Society criteria. Twenty-four patients had a PJI, and the remaining 81 patients were in the aseptic group. The microbiologic evaluation including polymicrobial infection showed C. (formerly P.) acnes in 15 patients (63%). Synovial fluid was then analyzed using microbiology cultures, alpha-defensin immunoassay, and leukocyte esterase. The specificity, sensitivity, and positive-predictive and negative-predictive values were calculated for each test.

Results
The overall accuracy for alpha-defensin was 91% (95% confidence interval [CI], 84.4–96); sensitivity was 75% (95% CI, 53–90), specificity was 96% (95% CI, 90–99), negative predictive value was 93% (95% CI, 85–97), and positive predictive value was 86% (95% CI, 64–97). In contrast, the overall accuracy for leukocyte esterase was 76% (95% CI, 61–88), sensitivity was 50% (95% CI, 21–79), specificity was 87% (95% CI, 69–96), positive predictive value 60% (95% CI, 26–88) and negative predictive value was 81% (95% CI, 64–93).

Conclusions
Summarizing the study results, the alpha-defensin ELISA and leukocyte esterase tests had less sensitivity in detecting shoulder PJI than previously reported TKA or THA results. The quality and low amount of joint fluid is the difficult part of the diagnostic. C. (formerly P.) acnes was the most common cause of PJI. Focusing on low-grade infections, alpha-defensin has shown its advantages in diagnosing PJI regardless pathogen virulence. Since the diagnostic of a PJI is always a synopsis of findings, the alpha-defensin and leukocyte esterase test can be used as adjunct diagnostic tool in patients with painful TSA. We propose further prospective studies to improve the diagnostic and confirm the results.

Level of Evidence
Level III, diagnostic study.