Background: Antibodies against phosphatidylserine/prothrombin (aPS/PT) have garnered considerable attention in the diagnosis of antiphospholipid syndrome (APS), especially the thrombotic type. A significant link has been established between aPS/PT antibodies and both thrombosis and pregnancy complications in patients with APS. This highlights the clinical value of including aPS/PT antibodies in the diagnostic process for APS, particularly in identifying patients at increased risk for thrombotic events and negative pregnancy outcomes.

Objectives: Here, we assess the relationship between aPS/PT antibodies with accrual damage in APS.

Methods: We conducted a monocentric exploratory cross-sectional study. The study included 143 patients fulfilling the ACR/EULAR 2023 classification criteria for APS. Immunoglobulin (Ig)G/IgM aPS/PT, IgG/IgM anticardiolipin (aCL), and IgG/IgM anti- β2 glycoprotein I (anti- β2 GPI) antibodies were detected using ELISA assay and lupus anticoagulant (LA) with a series of coagulation tests.

Results: IgG aPS/PT, but not IgM aPS/PT, was associated with both arterial and venous thrombosis events (p=0.036) concerning arterial or venous thrombosis alone (42.9% vs 34.9% vs 22.2%). There was no difference between IgG/IgM aPS/PT and obstetric APS subsets. IgG and IgM aPS/PT were significantly associated with the microvascular domain (p=0.01 and p= 0.005, respectively), while IgG aPS/PT was associated with valvulopathy (p= 0.022). Both triple aPL positivity (IgG/IgM aCL+IgG/IgM anti- β2 GPI +LA) and quadruple aPL positivity (IgG/IgM aCL+IgG/IgM anti- β2 GPI +LA) were associated with accrual damage (p=0.035 and p= 0.003, respectively). However, at the multivariate logistic regression, only quadruple aPL showed a 4-fold risk of accrual damage in APS patients (OR 4.2, 95%IC 1.1-16.4, p=0.038).

Conclusion: Our data attribute clinical relevance to both IgG and IgM aPS/PT antibodies. Both were associated with more severe APS subsets, such as arterial and venous thrombosis, as well as the microvascular and valvulopathy domains. Moreover, quadruple aPL positivity was associated with accrual damage, suggesting their utility in risk stratification in APS patients.

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[2] Hoxha A, Mattia E, Tonello M, Grava C, Pengo V, Ruffatti A. Antiphosphatidylserine/prothrombin antibodies as biomarkers to identify severe primary antiphospholipid syndrome. Clin Chem Lab Med. 2017 May 1;55(6):890-898 doi: 10.1515/cclm-2016-0638.

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Acknowledgements: NIL.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.