Diagnostic Accuracy of Alpha-Defensin Lateral Flow Assay in Total Hip and Knee Arthroplasty.

Abstract

Accurate diagnosis of periprosthetic joint infection (PJI) remains suboptimal. Of the tests used, one is the alpha defensin lateral flow assay (ADLFA). This study assessed ADLFA for the diagnosis of PJI in total hip arthroplasties (THAs) and total knee arthroplasties (TKAs). We hypothesized that ADLFA would have high specificity and sensitivity for diagnosing PJI, but that certain clinical features would influence test reliability. We reviewed 473 ADLFA tests from 141 THAs and 332 TKAs performed from 2020 to 2023 at a single institution. The mean age was 66 years, 51% were women, and mean BMI was 32. There were 142 PJIs (2018 Musculoskeletal Infection Society criteria excluding ADLFA). Overall, 49% were primary and 51% revision procedures, 22% were on antibiotics within two weeks of arthrocentesis, 18% had an inflammatory arthropathy, and 7% had an in situ spacer. The overall sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ADLFA were 80, 97, 92, and 92%, respectively. There were 6% (29 of 473) that had false negative results, of which 38% were on antibiotics within two weeks of arthrocentesis and 21% of which were spacer aspirations. The NPV was lower for those who had recent antibiotic use (76%) compared to those who did not (94%; P < 0.001). There was lower sensitivity (57%) for spacer compared to non-spacer aspirations (82%; P = 0.04). Furthermore, sensitivity in THA (67%) was lower compared to TKA (84%; P = 0.033). In TKAs, there was lower specificity (91%) for those who had inflammatory arthropathies (99%; P = 0.02). The ADLFA is highly specific in diagnosing PJI and is less sensitive in patients who have antibiotic spacers and those who have THAs compared to TKAs. Additionally, underlying inflammatory arthropathies may decrease specificity, yielding false positive results, specifically in TKAs.