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. 2025 Oct 4;6(5):e70154.
doi: 10.1002/jha2.70154. eCollection 2025 Oct.

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

Sofia Camerlo  1   2 , Massimo Radin  3 , Giorgio Rosati  1 , Melissa Padrini  1 , Barbara Montaruli  4 , Isabella Russo  1 , Cristina Barale  1 , Alice Barinotti  3 , Irene Cecchi  3 , David Galarza  5 , Fulvio Pomero  2 , Marco De Gobbi  1 , Savino Sciascia  3 , Alessandro Morotti  1
Affiliations

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

Sofia Camerlo et al. EJHaem. .

Abstract

Introduction: 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).

Discussion: 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.

Conclusion: 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.

Trial registration: The authors have confirmed clinical trial registration is not needed for this submission.

Keywords: antiphospholipid syndrome; immune thrombocytopenia; phosphatidylserine/prothrombin antibodies.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Overview of the screening and selection process for patients included in the study. The flow chart of patient's enrolment and analysis is indicated for each individual group.
FIGURE 2
FIGURE 2
Mean platelet count in patients with aPL‐negative, aPL‐positive ITP, and ITP secondary to APS. Indication of platelets number in the indicated cohort of patients.
FIGURE 3
FIGURE 3
Severity of thrombocytopenia in patients with aPL‐negative, aPL‐positive ITP, and ITP secondary to APS. Distribution of platelet severity in the cohort of patients. The degree of severity of thrombocytopenia is classified as follows: mild (platelet count < 100,000 and ≥ 50,000/µL), moderate (< 50,000, and ≥ 20,000/µL) and severe (< 20,000/µL).
See this image and copyright information in PMC

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