Prevalence of antiphospholipid antibody syndrome misclassification in an academic health system

Purpose: Antiphospholipid Antibody Syndrome (APS) is a complex autoimmune disorder that includes a com-bination of laboratory criteria and clinical events (thrombosis, pregnancy complications). Accurate classification is essential, as APS patients may have limited oral anticoagulant options and requires indefinite anticoagulation. The prevalence of inaccurate APS misclassification is unknown. This study sought to determine the proportion of patients in an academic health-system who formally met APS criteria.Methods: This retrospective cohort study included any patient within the University of Utah Health system who had an International Classification of Diseases-10 code for APS, between January 1, 2016 and June 30, 2020. Manual chart review was performed to assess the appropriateness of the APS classification by laboratory and clinical criteria.Results: Of the 184 patients identified, 59 (32.1 %) formally met APS criteria, while 69 (37.5 %) did not meet criteria. The remaining 56 (30.4 %) patients lacked enough information in their medical records to decide on appropriateness of APS classification. The most prevalent reason for inappropriate APS classification in the 69 patients identified was incorrect interpretation of lab values as positive (62; 89.9 %), followed by lack of repeat confirmation testing (32; 46.4 %).Conclusion: The results of this single-center study indicate that only one-third of patients with presumed APS met classification criteria. This was predominantly due to incorrect collection or interpretation of APS laboratory data. One-third had insufficient medical record data to determine APS classification, which impairs clinical decision-making. This suggests more education or implementation of anticoagulation stewardship is needed to ensure accurate APS classification and proper management of anticoagulation therapy.