Good accuracy of the alpha-defensin lateral flow test for hip periprosthetic joint infection: A pilot study in a retrospective cohort of 52 patients

BACKGROUND: The alpha-defensin lateral flow (ADLF) test is a new diagnostic tool for periprosthetic joint infection (PJI). Test accuracy for combined cohorts of hip and knee PJI has been reported to be good. AIM: To assess the accuracy of the ADLF test for hip PJI, and to compare three different diagnostic criteria for PJI. METHODS: A cohort of 52 patients was identified, with a painful or poorly functioning total hip- or hemi-arthroplasty, that underwent aspiration and a subsequent ADLF test. PJI was diagnosed with Musculoskeletal Infection Society (MSIS) criteria, and sensitivity, specificity, overall accuracy, positive predictive value and negative predictive value were calculated. Furthermore, test specifics were compared with the European Bone and Joint Infection Society (EBJIS) and 2018 International Consensus Meeting (ICM) criteria for PJI. RESULTS: Using MSIS criteria, sensitivity was 100% (CI: 54%-100%) and specificity was 89% (CI: 76%-96%). Six true positives and 5 false positives were found, including one case of metallosis. Using EBJIS criteria, more PJIs were found (11 vs 6), sensitivity was lower (71%, CI: 42%-92%) and specificity was higher (97%, CI: 86%-100%), with 4 false negatives and one false positive result. Using 2018 ICM criteria, sensitivity was 91% (62%-100%) and specificity 100% (91%-100%). The results in this cohort are comparable to previous studies. CONCLUSION: Overall test accuracy of the ADLF test was good in this cohort, with a sensitivity of 100% and specificity of 89%. Using different PJI definition criteria, sensitivity and specificity changed slightly but overall accuracy remained around 90%. Using the ADLF test in metallosis cases can result in false positive results and should be performed with caution.