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How Reliable Is the Alpha-defensin Immunoassay Test for Diagnosing Periprosthetic Joint Infection? A Prospective
Tommaso Bonanzinga1, Akos Zahar2, Michael Dütsch1
1HELIOS ENDO Klinik, Holstenstrasse 2, 22767, Hamburg, Germany.
Background:
A key issue in the treatment of periprosthetic joint infection (PJI) is the correct diagnosis. The main problem is lack of diagnostic tools able to diagnose a PJI with high accuracy. Alpha-defensin has been proposed as a possible solution, but in the current literature, there is a lack of independent validation.
Questions/Purposes:
We performed a prospective study to determine (1) what is the sensitivity, specificity, and positive and the negative predictive values of the alpha-defensin immunoassay test in diagnosing PJI; and (2) which clinical features may be responsible for false-positive and false-negative results?
Methods:
Preoperative aspiration was performed in all patients presenting with a painful hip/knee arthroplasty, including both primary and revision implants. Metallosis, other inflammatory comorbidities, and previous/concomitant antibiotic therapy were not considered as exclusion criteria. An inadequate amount of synovial fluid for culture was an exclusion criterion. A total of 156 patients (65 knees, 91 hips) were included in this prospective study. At the time of revision, synovial fluid samples were taken to perform the alpha-defensin assay. During surgical débridement of tissue, samples for cultures and histologic evaluation were taken, and samples were cultured until positive or until negative at 14 days. A diagnosis of PJI was confirmed in 29 patients according to the International Consensus Group on PJI.
Results:
The sensitivity of the alpha-defensin immunoassay was 97% (95% confidence interval [CI], 92%-99%), the specificity was 97% (95% CI, 92%-99%), the positive predictive value was 88% (95% CI, 81%-92%), and the negative predictive value was 99% (95% CI, 96%-99%). Among four false-positive patients, two had metallosis and one had polyethylene wear. The false-negative case presented with a draining sinus, and intraoperative cultures were also negative.
Conclusions:
Alpha-defensin assay appears to be a reliable test, but followup evaluation is needed to estimate longer term performance of the test. The authors believe that alpha-defensin has demonstrated itself to be sufficiently robust that PJI diagnostic criteria now should include this test. Future studies are needed to compare the differences among the diagnostic capability of the available tests, in particular when metallosis is present, because metallosis may predispose the test to a false-positive result.
Level Of Evidence:
Level I, diagnostic study.
Insights
The alpha-defensin immunoassay shows high accuracy in diagnosing periprosthetic joint infection (PJI), demonstrating excellent sensitivity and specificity. This reliable test could be incorporated into diagnostic criteria for PJI.
Area of Science:
- Orthopedic Surgery
- Infectious Diseases
- Diagnostic Medicine
Background:
- Accurate diagnosis of periprosthetic joint infection (PJI) remains a significant challenge due to limitations in current diagnostic tools.
- Alpha-defensin has emerged as a potential biomarker for PJI, but independent validation is scarce in existing literature.
Purpose of the Study:
- To prospectively evaluate the diagnostic performance of the alpha-defensin immunoassay for PJI.
- To determine the sensitivity, specificity, positive predictive value, and negative predictive value of the alpha-defensin test.
- To identify clinical factors contributing to false-positive and false-negative results in PJI diagnosis.
Main Methods:
- A prospective study involving 156 patients (65 knees, 91 hips) with painful arthroplasty underwent preoperative synovial fluid aspiration.
- Synovial fluid samples were analyzed using the alpha-defensin immunoassay, and intraoperative samples were collected for cultures and histology.
- Periprosthetic joint infection diagnosis was confirmed in 29 patients based on the International Consensus Group criteria.
Main Results:
- The alpha-defensin immunoassay demonstrated high diagnostic accuracy with 97% sensitivity and 97% specificity.
- Positive and negative predictive values were 88% and 99%, respectively, indicating strong test reliability.
- Metallosis and polyethylene wear were identified in false-positive cases, while a draining sinus was noted in the false-negative case.
Conclusions:
- The alpha-defensin assay is a reliable diagnostic tool for periprosthetic joint infection (PJI).
- The study suggests incorporating the alpha-defensin test into established PJI diagnostic criteria.
- Further research is recommended to assess long-term performance and compare its efficacy against other tests, especially in cases involving metallosis.
