Severe thrombocytopenia is associated with arterial thrombotic manifestations in antiphospholipid syndrome: a two-center cohort study

Objective Thrombocytopenia in APS is often regarded primarily as a bleeding-related manifestation, but the relationship between platelet-count severity and thrombotic manifestations remains uncertain. We evaluated the association between severe thrombocytopenia and arterial thrombotic manifestations in patients with antiphospholipid syndrome (APS). Methods In a two-center baseline cohort of 313 patients with APS, baseline platelet count (PLT) was categorized as PLT <50×10 9 /L, PLT 50–<100×10 9 /L, or PLT ≥100×10 9 /L. Associations with prevalent baseline thrombotic manifestations were assessed using multivariable logistic regression in 300 patients with primary APS or systemic lupus erythematosus-associated APS. In the Renji follow-up cohort (n=254), 48-month thrombotic events were evaluated using Kaplan–Meier curves and Cox models. Results PLT <50×10 9 /L was associated with a higher frequency of arterial thrombosis (66.7%), particularly cerebral infarction (62.7%), whereas venous thrombosis was most frequent in the PLT 50–<100×10 9 /L group (68.4%). After multivariable adjustment, PLT <50×10 9 /L remained associated with a higher prevalence of arterial thrombosis (aOR 2.16, 95% CI 1.07–4.35, P = 0.032) and cerebral infarction (aOR 2.37, 95% CI 1.18–4.73, P = 0.015). During 48-month follow-up, PLT <50×10 9 /L was associated with increased risks of any thrombotic event (HR 3.28, 95% CI 1.54–6.97, P = 0.002), arterial thrombotic event (HR 3.95, 95% CI 1.39–11.21, P = 0.010), and cerebral infarction (HR 4.11, 95% CI 1.44–11.73, P = 0.008), but not venous-related events. Conclusion Severe thrombocytopenia was associated with arterial thrombotic manifestations in APS, particularly cerebral infarction. PLT <50×10 9 /L may provide additional clinical risk information but may also reflect cumulative disease burden and overall APS severity.