Elsevier

The Journal of Arthroplasty

Volume 36, Issue 8, August 2021, Pages 2957-2961
The Journal of Arthroplasty

Complications - Infection
The Alpha-Defensin Prosthetic Joint Infection Test Has Poor Validity for Native Knee Joint Infection

https://doi.org/10.1016/j.arth.2021.03.020Get rights and content

Abstract

Background

The alpha-defensin test known as Synovaure has been very effective in diagnosis of prosthetic joint infections (PJIs). Being able to easily and accurately differentiate septic and inflammatory arthropathies in native joints would improve diagnostic workup and management. We tested the ability of an alpha-defensin test to distinguish septic from inflammatory or crystalline arthropathy in the native knee.

Methods

40 native knee joint fluid specimens were tested with cell count, fluid analysis, and culture and alpha-defensin testing. We determined the sensitivity and specificity of the alpha-defensin test using culture-positive fluid as the gold standard for septic arthropathy and positive crystals as the gold standard for crystalline arthropathy.

Results

The Synovasure PJI test had 100% specificity for septic arthritis coupled with a 28% false-positive rate when applied to native knee aspirations. False-positive rate was 5.3 times higher in patients with crystals found in the joint fluid.

Conclusion

Alpha-defensin testing, in the form of the Synovasure PJI test, has a high-false-positive rate when used to distinguish septic and inflammatory arthritis in the native knee joint. Future work will need to determine the sensitivity and specificity of the newer native joint panel. Clinicians should be cognizant of the specific alpha-defensin test used when sampling native knee synovial fluid.

Section snippets

Materials and Methods

Institutional review board approval was obtained for this retrospective study. Every knee joint aspiration performed in our institution from March 2017 to March 2018 was reviewed. Inclusion criteria for the study included native joints, patients over the age of 18 years, and specimens sent for alpha-defensin testing. Patients below 18 years of age, aspirations from prosthetic joints, and inadequate samples, such as those not sent for alpha defensin or hemolyzed samples, were excluded. Recent

Results

The 40 study subjects ranged in age from 34 to 96 years, with a mean (standard deviation) of 56.2 (14.1) years of age. Twenty-eight (70%) were men. Table 1 shows patient demographics classified by alpha-defensin assay result. White non-Hispanics were overrepresented at 71% in the assay-positive group vs 46% in the assay-negative group, whereas African Americans were correspondingly overrepresented at 50% in the assay-negative group vs 14% in the assay-positive group (P = .051). Age and sex,

Discussion

The results of this study indicate that the Synovasure PJI test has 100% sensitivity but a 28% false-positive rate for detection of septic arthritis in native joints, with a NPV of 100% and a PPV of only 29%. The Synovasure assay was positive in 64% infection-free samples with crystals present and positive in 12% of infection-free samples with crystals absent, indicating poor sensitivity and specificity in detecting crystalline arthritis.

The ability to accurately detect septic vs inflammatory

Conclusions

The Synovasure PJI assay does not accurately diagnose native joint septic arthritis nor provide utility in distinguishing septic vs crystalline arthritis. Our results show that PJI Synovasure testing has a high-false-positive rate when crystalline arthropathy occurs in native joints. We do not recommend its use in diagnostic studies of native joints and are hopeful that improvements in the immunoassay panel will improve diagnosis of native joint infections in the future.

Acknowledgments

None.

References (19)

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Cited by (2)

  • Procedures for collection, transport and synovial fluid analysis in cases of suspected septic arthritis

    2022, Revue du Rhumatisme Monographies

  • The Ratio of IL-6 to IL-4 in Synovial Fluid of Knee or Hip Performances a Noteworthy Diagnostic Value in Prosthetic Joint Infection

    2022, Journal of Clinical Medicine

Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2021.03.020.

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