Baseline Laboratory Parameters Potentially Associated with Thrombophilia in Patients with Chronic ITP.

The concept that chronic immune thrombocytopenia (cITP) may be pro-thrombotic has progressively gained acceptance as reports show an increased risk of thromboembolism (TEE) among cITP patients. A report from the Danish National Patient Registry showed an incidence of venous TEE of 5.32/1000 patient years (PYs) among cITP patients and 2.04/1000 PYs in a reference cohort (Severinsen 2010). Similar results were found in a US claims database study (Bennett 2008). ITP experts have gradually acknowledged this higher risk, but the reason for it is not understood. Many hematologic markers have been shown to be indicators of thrombophilia or activation of the clotting cascade (Jenkins 2012; De Stefano 2002; Tsai 2002); to our knowledge they have not been systematically and prospectively studied in cITP patients.

Describe the frequency of potential laboratory predictors of thrombophilia in cITP.

Adults with cITP were enrolled in an ongoing study to evaluate effects of eltrombopag on the bone marrow. A “thrombophilia panel” of suspected/known indicators of a thrombophilic state or activation of the coagulation cascade was collected at baseline. Patients could not have been treated with thrombopoietin receptor (TPO-R) agonists 6 months prior to enrollment. Patients with history of TEE and ≥2 risk factors for thrombosis were not eligible for enrollment.

Baseline thrombophilia panels were available for all 167 patients. Median age was 41 years; 108 (65%) patients were female. Approximately half of the patients were Caucasians (48.5%), while 31.1% and 19.2% had Central South and East Asian heritage. Median time since ITP diagnosis was 3.9 years (range, 0.2–45.7). Thirteen (8%) patients reported prior exposure to TPO-R agonists. Most patients (95%) had no family history of TEE and no patient had a history of TEE. Most patients (81%; Table 1) had abnormal levels of at least one well-known or suspected predictor of thrombosis or marker of activation of the coagulation cascade, and 93 (56%) had >1 abnormality. The most frequent abnormalities were elevated Factor VIII (48%), elevated d-dimer (32%), lupus anticoagulant (26%), and deficient protein S (22%; Table 2).

To our knowledge this is the only published prospective study of a thrombophilia profile in a cohort of cITP patients. Recently published data suggest that patients with cITP have a higher risk of TEE but no adequate explanation for this has been furnished. The fact that a high proportion of patients in this study had markers of thrombophilia or activation of clotting provides a working hypothesis that may at least partially elucidate this trait.

The multiple baseline abnormalities in possible predictors of thrombophilia may support the theory that ITP is pro-thrombotic, but they need to be assessed in and compared to the general population to allow proper understanding of their implications. The potential correlation of these abnormalities with TEE in this cohort will be reported upon study conclusion.

Wong:GlaxoSmithKline: Research Funding; Pfizer: Research Funding; Biogen-Idec: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bayer: Consultancy, Research Funding; Johnson & Johnson: Research Funding; MSD: Research Funding; Roche: Research Funding; Bristol-Myers Squibb: Research Funding. Bakshi:GlaxoSmithKline: Employment, Equity Ownership. Brainsky:GlaxoSmithKline: Employment, Equity Ownership, Patents & Royalties.