Abstract
Aim
The aim of the study was to assess the accuracy of the alpha defensin lateral flow test for diagnosis of periprosthetic joint infection (PJI) using an optimized diagnostic algorithm and three classification systems. In addition, we compared the performance with synovial fluid leukocyte count, the most sensitive preoperative test.
Method
In this prospective multicenter study we included all consecutive patients with painful prosthetic hip and knee joints undergoing diagnostic joint aspiration. Alpha defensin lateral flow test was used according to manufacturer instructions. The following diagnostic criteria were used to confirm infection: Musculoskeletal Infection Society (MSIS), Infectious Diseases Society of America (IDSA) and Swiss orthopedics and Swiss Society of Infectious Diseases (SOSSID). In the latter, PJI was confirmed when at least one of following criteria applied: macroscopic purulence, sinus tract, positive cytology of joint aspirate (>2000 leukocytes/μl or >70% granulocytes), histological proof of acute inflammation in periprosthetic tissue, positive culture (from aspirate, tissue or sonication fluid). Infection was classified as chronic, if symptom duration was more than 3 weeks or if infection manifested after more than 1 month after surgery. The sensitivity and specificity of the alpha defensin lateral flow test and leukocyte count in synovial fluid were calculated and compared using McNemar Chi-square test.
Results
Of 151 included patients evaluated for painful prosthetic joints (103 involved knees, 48 hips), the median patient age was 69 years (range, 41–94 years) and 75 patients were female. Systematically evaluating the included patients according to the different diagnostic criteria, MSIS and IDSA revealed both 33 patients with PJI (22%), whereas SOSSID disclosed 47 septic failures (31%), among them 36 chronic infections (77%). Sensitivity of the test was 79% when applying MSIS criteria, 70% with IDSA criteria and 57% with SOSSID criteria. Specificity ranged from 96% (IDSA) to 98% (MSIS) and 99% (SOSSID). Applying the most stringent definition criteria (SOSSID), leukocyte count showed significantly higher sensitivity than the alpha defensin lateral flow test (91% vs. 57%, p<0.001), especially in chronic infections (88% vs. 48%, p<0.001.) In acute infections, both tests detected all infection cases. Processing turnaround time was shorter in Alpha defensin lateral flow test than automated leukocyte count (10 min vs. 2–4 hours)
Conclusions
Semi-quantitative alpha defensin test was rapid and highly specific for diagnosing PJI (> 95%). However, sensitivity was limited, especially when applying definition criteria including also low grade infections (SOSSID criteria). Therefore, the alpha defensin lateral flow test does not allow a reliable exclusion of PJI, especially not in chronic infections but may be used as confirmatory test.
