Highlight
Key points
– In a prospective international registry of 1,067 persistently antiphospholipid antibody (aPL)–positive patients (APS ACTION), history of thrombosis and hematologic disease (autoimmune hemolytic anemia and/or thrombocytopenia) independently predicted new thrombotic events (≈2‑fold increased risk each).
– Over a mean 4.43 years (4,727 person‑years) of follow‑up there were 93 incident thrombotic events; several additional clinical factors (microvascular disease, obesity, renal disease, sedentary lifestyle) were more common among patients who developed thrombosis, though these did not remain independent predictors after adjustment.
Background
Antiphospholipid syndrome (APS) is an acquired thrombophilia characterized by venous, arterial or microvascular thrombosis and/or pregnancy morbidity in the presence of persistent antiphospholipid antibodies (aPL). Risk stratification for primary and secondary thrombosis prevention in persistently aPL‑positive patients is an unmet need. Clinicians must weigh the risks of anticoagulation or antiplatelet therapy against bleeding and comorbidity in a heterogeneous population. High-quality prospective data identifying which clinical and biologic features predict new thrombotic events are therefore essential to inform individualized preventive strategies and to design trials that target those at greatest residual risk.
The International APS ACTION Clinical Database and Repository (APS ACTION Registry) enrolls patients who meet the Revised Sapporo Classification Criteria for APS and follows them prospectively, providing an opportunity to examine predictors of incident thrombosis among persistently aPL‑positive patients across multiple centres.
Study design
This analysis used APS ACTION Registry data and included registrants with at least 1 year of follow‑up. Inclusion required persistent aPL positivity per the Revised Sapporo Classification Criteria. The analytic cohort comprised 1,067 patients with a mean follow‑up of 4.43 years, contributing 4,727 person‑years. Incident thrombotic events were the primary outcome; 93 patients developed new thrombosis during follow‑up.
Investigators compared baseline clinical and biologic characteristics between those who did and did not develop new thrombosis. They used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for predictors of incident thrombosis, reporting unadjusted differences and multivariable‑adjusted independent associations.
Key findings
Patient population and outcome
– Cohort size: 1,067 persistently aPL‑positive patients.
– Mean follow‑up: 4.43 years.
– Total person‑years: 4,727.
– Incident thrombotic events: 93 (new thrombosis); 974 patients had no new thrombosis.
Unadjusted associations
In univariate comparisons, several baseline characteristics occurred more commonly among patients who subsequently experienced a new thrombosis (P < .05):
– History of thrombosis (prior thrombotic events)
– Hematologic disease — defined here as autoimmune hemolytic anemia and/or thrombocytopenia
– Microvascular disease
– Obesity
– Renal disease
– Sedentary lifestyle
– Baseline anticoagulant use
– Family history of premature cardiovascular disease
These unadjusted differences highlight candidate clinical risk factors that may mark higher thrombosis propensity in persistently aPL‑positive patients.
Adjusted (multivariable) predictors
After multivariable adjustment, two factors remained independently associated with increased risk of new thrombosis:
– History of thrombosis: HR 2.34 (95% CI 1.14 to 4.81), P = .02. Patients with prior thrombotic events had approximately a 2.3‑fold higher hazard of subsequent thrombosis compared with those without prior thrombosis.
– Hematologic disease (autoimmune hemolytic anemia and/or thrombocytopenia): HR 1.95 (95% CI 1.19 to 3.18), P = .01. Presence of these hematologic complications nearly doubled the risk of new thrombosis.
There were non‑statistically significant trends for two other factors after adjustment:
– History of microvascular disease: P = .06 (trend toward increased risk).
– Obesity: P = .08 (trend toward increased risk).
Interpretation of baseline anticoagulant association
Baseline anticoagulant use was more common among those who developed incident thrombosis in unadjusted analyses. This likely reflects confounding by indication — patients with prior thrombosis (and therefore higher baseline anticoagulant use) are at intrinsically higher risk of recurrent events. Multivariable adjustment, which included history of thrombosis, attenuated that association.
Magnitude and clinical relevance
The adjusted effect sizes indicate that two readily ascertained clinical variables — prior thrombosis and hematologic disease — identify subgroups of persistently aPL‑positive patients at roughly double the risk of future thrombosis. Given the absolute event rate (93 events across 4,727 person‑years), these relative risks translate into clinically meaningful differences in absolute risk that could inform decisions about intensified monitoring or preventive therapy in high‑risk patients.
Expert commentary and mechanistic considerations
Why might hematologic disease increase thrombosis risk in aPL‑positive patients?
Autoimmune hemolytic anemia and immune thrombocytopenia (ITP‑type processes) can coexist with aPL positivity. Several mechanistic pathways plausibly link hematologic disease to thrombosis: hemolysis releases procoagulant cell‑free hemoglobin and red‑cell microvesicles that promote oxidative stress and platelet activation; immune‑mediated platelet destruction can be accompanied by platelet activation and the release of procoagulant microparticles; and complement activation — commonly implicated in both hemolysis and APS pathogenesis — amplifies thromboinflammation. Thus, even when platelet counts are reduced, qualitative platelet activation and procoagulant microparticles may increase thrombosis risk.
History of thrombosis as a predictor
A prior thrombotic event is a well‑recognized marker of future risk in many thrombotic disorders, reflecting both a stable predisposition and possible incomplete mitigation of that predisposition by therapy. In APS, recurrent thrombosis can occur despite anticoagulation in some patients; prior thrombosis may therefore identify biological phenotypes (for example, high‑titer antibodies, triple positivity, or concomitant inflammation) that confer persistent risk.
Microvascular disease and obesity
Microvascular disease showed a trend toward association with incident thrombosis. Microvascular manifestations (e.g., livedo reticularis, small‑vessel occlusions) may reflect an active systemic prothrombotic state. Obesity is a well‑established prothrombotic condition via inflammation, impaired fibrinolysis, and endothelial dysfunction; the observed trend (P = .08) is biologically plausible and may warrant attention in risk models.
Limitations to consider
– Observational registry data may be affected by residual confounding and indication bias (e.g., anticoagulant prescriptions reflect prior events).
– The registry predominantly enrolls patients from specialized centers; results may not be fully generalizable to community settings.
– The report focuses on clinical predictors; detailed serologic variables (e.g., lupus anticoagulant status, aCL/aβ2GPI titers, single vs triple positivity) are central to APS risk but their independent predictive value in this analysis is not the principal focus of the presented summary.
– Event adjudication, therapy intensity (target INR, anticoagulant class), and adherence details influence outcomes but may vary across centers.
Clinical and research implications
For clinicians
– Patients with persistent aPL positivity who have a prior thrombosis should be considered at substantially higher risk for recurrence and may warrant intensified surveillance and individualized secondary prevention plans.
– The coexistence of autoimmune hemolytic anemia or immune thrombocytopenia in aPL‑positive patients identifies a higher‑risk subgroup that may merit closer follow‑up and multidisciplinary management (hematology + rheumatology). Consideration of modifiable risk factors (weight management, activity, BP and lipid control, smoking cessation) remains important.
For researchers and trialists
– These findings can be used to enrich clinical trials of thrombosis prevention in persistently aPL‑positive patients by targeting higher‑risk subgroups (history of thrombosis and hematologic disease), increasing event rates and statistical power.
– Future models should prospectively integrate serologic profiles (lupus anticoagulant, aCL/aβ2GPI isotypes and titers, persistent triple positivity), biomarkers of platelet activation and complement activation, and clinical variables to develop validated risk scores.
Conclusion
In the international APS ACTION Registry prospective cohort of 1,067 persistently aPL‑positive patients followed for a mean of 4.43 years, a history of thrombosis and the presence of hematologic disease (autoimmune hemolytic anemia and/or thrombocytopenia) were independent predictors of new thrombotic events, each conferring an approximately twofold increased hazard. Other clinical factors such as microvascular disease and obesity showed trends toward increased risk. These pragmatic clinical predictors can guide risk‑stratified surveillance, inform shared decision‑making regarding preventive strategies, and serve as criteria for enriching clinical trial populations.
Funding and clinicaltrials.gov
Funding details and clinicaltrials.gov registration were not specified in the summary provided. The full manuscript (Thaler et al., Ann Rheum Dis. 2025) should be consulted for funding sources, detailed methods, and any trial registry identifiers.
Selected references
– Thaler J, Parides M, de Andrade DCO, Ruiz DP, Tektonidou MG, Pengo V, et al. Clinical and biologic predictors of thrombosis in persistently antiphospholipid antibody‑positive patients: Prospective analysis of the International APS ACTION Clinical Database and Repository (‘Registry’). Ann Rheum Dis. 2025 Nov 19. doi: 10.1016/j.ard.2025.10.019. Epub ahead of print. PMID: 41266210.
– Miyakis S, Lockshin MD, Atsumi T, Branch DW, Brey RL, Cervera R, et al. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS). J Thromb Haemost. 2006;4(2):295–306.
(Note: readers should consult the full published article for complete methodology, serologic analyses, treatment details, and supplementary data.)