The Accuracy of the Alpha Defensin Lateral Flow Device for Diagnosis of Periprosthetic Joint Infection: Comparison with a Gold Standard

Background: Alpha defensin is a new biomarker that has been shown to have a very high accuracy to rule out peri-prosthetic joint infection. Recently, a new rapid lateral flow version of the alpha defensin test was developed and introduced to detect high levels of alpha defensin in synovial fluid quickly and with ease. We conducted a single-center prospective clinical study to compare the results of the Synovasure Alpha Defensin Test with those of the Musculoskeletal Infection Society (MSIS) criteria, which are considered to be the gold standard for diagnosing periprosthetic joint infection.Methods: A total of 223 consecutive patients with pain after total hip arthroplasty or total knee arthroplasty were enrolled into the study. In all patients, blood C-reactive protein was measured and joint aspirations were performed. From the synovial fluid, a leukocyte cell count with granulocyte percentage, microbiology cultures, and leukocyte esterase tests were carried out according to the recommendation of the MSIS for diagnosing periprosthetic joint infection. Concurrently, the Synovasure Alpha Defensin Test with a lateral flow device was performed from the aspirate. In the final clinical and statistical evaluation, 191 subjects with 195 joint aspirations (96 hips and 99 knees) were included. According to the MSIS criteria, there were 119 joints with an aseptic revision and 76 joints with periprosthetic joint infection.Results: After statistical analysis, the overall sensitivity of the Synovasure Alpha Defensin Test was 92.1% (95% confidence interval [CI], 83.6% to 97.1%), the specificity was 100% (95% CI, 97.0% to 100%), the positive predictive value was 100% (95% CI, 94.9% to 100%), and the negative predictive value was 95.2% (95% CI, 89.9% to 98.2%). The overall accuracy of the Synovasure test was 96.9% (95% CI, 93.4% to 98.9%), 189 of 195 cases.Conclusions: Our results suggest that the Synovasure periprosthetic joint infection test has a very high accuracy in diagnosing periprosthetic infections after total hip arthroplasty or total knee arthroplasty. Although the Synovasure Alpha Defensin Test does not provide information on the identity of the infectious pathogen, the test does have an important role in recognizing periprosthetic joint infection early and enables surgeons to start proper therapy without delay.