Anti-Phosphatidylserine/Prothrombin Antibodies Identify a Distinct Form of ITP.

Immune thrombocytopenia (ITP) and antiphospholipid syndrome (APS) are distinct autoimmune disorders with clinical intersections. While APS is marked by thrombosis and pregnancy complications, ITP typically presents as isolated low platelet counts with bleeding risk. Thrombocytopenia can also occur in APS, and a subset of ITP patients test positive for antiphospholipid antibodies (aPL). This study examined aPL in 90 ITP patients and compared them to 132 APS patients. Among the ITP group, 18.3% were aPL-positive, with lupus anticoagulant most common; 12% had anti-phosphatidylserine/prothrombin (aPS/PT) antibodies. In the APS cohort, 16% exhibited thrombocytopenia (< 100,000/µL), with a mean platelet count of 44,000/µL, and 71% of these were positive for aPS/PT. Platelet levels varied significantly among ITP aPL-negative, ITP aPL-positive and APS-ITP groups (p < 0.001). aPL positivity was linked to less severe thrombocytopenia but affected treatment approaches, showing differences in first-line (p = 0.034) and second-line (p = 0.025) therapies. Patients with ITP secondary to APS had a higher mean platelet count compared to aPL-positive ITP patients and aPL-negative ITP patients. Screening for aPL and aPS/PT is vital to identify an ITP subset with milder thrombocytopenia and increased thrombotic risk, and may guide therapeutic decisions such as between thrombopoietin receptor agonists and SYK inhibitor. The authors have confirmed clinical trial registration is not needed for this submission.