Application of ACR/EULAR Classification Criteria in real life: thrombotic patients positive for Lupus Anticoagulant only

Objective/Aim. Lupus Anticoagulant (LA) positive only (negative for anticardiolipin antibodies [aCL] and anti-β2 glycoprotein I antibodies [aβ2GPI]) and thrombosis represents a clinical challenge. It is often unclear whether the cause of thrombosis is LA or whether other clinical conditions have led to an episode of venous thromboembolism (VTE) or arterial thromboembolism (ATE). Recent APS classification criteria assign different scores to thrombotic events based on the presence of confounding risk factors. In the presence of strong associated risk factors, patients are not classified as having APS as a score less than the 3-point is assigned to the clinical domain. Methods. This study evaluated patients LA positive only included in the group of Antiphospholipid Syndrome (APS) in the START2 Antiphospholipid Registry. Aim of the study was to determine how many of them did not meet the new APS classification criteria due to the presence of associated risk factors. Results. Eighty-six (18%) of the 488 patients enrolled in the START Antiphospholipid Registry had positive LA only and 43 had a previous thromboembolic event (33 VTE and 10 ATE). Three of the 33 patients with VTE (9%) had a high-risk VTE profile and 2 had a high-risk ATE profile and did not meet the new classification criteria. Conclusion. The updated criteria appropriately limit the inclusion of patients with high-risk thrombotic profiles in APS research studies. Although risk factors and not LA may be the cause of thrombosis, the presence of LA can complicate treatment decisions in clinical practice.

Publication History

Received: 16 July 2025

Accepted after revision: 21 October 2025

Accepted Manuscript online:
28 October 2025