Lupus Anticoagulant Testing in Challenging Situations: Navigating Complexities

ABSTRACT The laboratory diagnosis of antiphospholipid syndrome (APS) relies on detecting persistent antiphospholipid antibodies (aPL), including lupus anticoagulant (LA) as one of the three laboratory criteria. LA is a well‐established risk factor in APS and the cornerstone of APS diagnosis, identifying triple‐positive patients. LA testing is supported by testing guidelines, but challenges remain with LA measurement, which is complex and susceptible to numerous pitfalls and interferences. A nuanced understanding of the technical and interpretative aspects of LA testing is crucial for accurate diagnosis. Limited to specific patient populations, the timing of testing in relation to clinical events is essential to avoid false results, and only persistent LA positivity is considered diagnostic. Proper sample preparation, choice of assays, test procedure, cutoff values, and strategies to handle anticoagulant therapy interference pose significant challenges in LA testing. While advances in the harmonization of test procedures and testing guidelines have improved diagnostic reliability, the complex nature of LA demands careful consideration of methodological issues and potential interferences, underscoring the importance of expertise and interdisciplinary communication in achieving accurate results. Interpretative comments and close interaction between clinical pathologists and clinicians are mandatory for diagnosis and patient management. This paper will focus on the technical aspects of the laboratory method and the interpretation of LA results in the diagnosis of APS with attention to specific situations where LA testing is difficult.