Abstract

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disease characterised by elevated peripheral platelet destruction and inadequate platelet production. Little published epidemiological data exists concerning the risk of thromboembolic events (TE) among adult patients with ITP.

The objective of our investigation was to estimate the risk of TE among adult patients with and without ITP in the United Kingdom (UK) General Practice Research Database (GPRD), which contains patient data from 6.4 million patients from more than 480 representative medical practices across the UK.

Using read [2871C] or Oxford Medical Information System (OXMIS) [D3130000, D313012, 42P2.11, D313.12] codes to define cases, incidence rates (IRs) per 10,000 patient-years of observation (PYO) with 95% confidence intervals (CIs) were estimated. Hazard ratios (HRs) of venous, arterial, and combined (venous and arterial) TE were modelled using Cox proportional hazards regression adjusting for history of prior TE, hypertension, splenectomy status, oral corticosteroids and intravenous immunoglobulin exposure.

840 adults (≥ 18 years) with codes for ITP first referenced between January 1, 1992 and September 30, 2005 and having at least one year pre-diagnosis and three months of post-diagnosis medical history were matched with 3,360 non-ITP patients by age, gender, primary care practice and pre-study follow-up time. Over a median 52 months of follow-up (range: 3–182 months), the cumulative incidence of TE among thromboembolic-free patients at baseline was higher within the ITP cohort [47 (6.7%) v. 172 (5.7%)]. As shown in the table below, the IRs of venous, arterial, and combined TE were additionally elevated among patients with ITP.

Outcome Incidence Rate/10,000 PYO 95% CI 
 Adult Patients with ITP Adult Patients without ITP 
Venous TE 70.83 (46.67–103.05) 47.53 (37.39–59.58) 
Arterial TE 82.02 (55.73–116.42) 71.50 (58.87–86.04) 
Combined TE 134.74 (99–179.18) 116.32 (99.59–135.06) 
Outcome Incidence Rate/10,000 PYO 95% CI 
 Adult Patients with ITP Adult Patients without ITP 
Venous TE 70.83 (46.67–103.05) 47.53 (37.39–59.58) 
Arterial TE 82.02 (55.73–116.42) 71.50 (58.87–86.04) 
Combined TE 134.74 (99–179.18) 116.32 (99.59–135.06) 

Adjusted HRs of 1.58 (95% CI, 0.98–2.53), 1.02 (95% CI, 0.65–1.59), and 1.17 (95% CI, 0.82–1.66) were found for venous, arterial, and combined TE respectively. Further event categorisation revealed elevated HRs for each venous thromboembolic subtype [deep vein thrombosis 1.49 (95% CI, 0.62–3.61), pulmonary embolism 3.52 (95% CI, 1.23–10.04), and other TE 1.17 (95% CI, 0.64– 2.16)].

This study provides evidence of an increased risk in venous TE in adult patients with ITP relative to the general adult non-ITP population.

Disclosures: Sarpatwari:GSK: Consultancy, Research Funding; Baxter: Honoraria, Membership on an entity’s Board of Directors or advisory committees. Bennett:GSK: Employment. Logie:GSK: Employment. Beach:GSK: Employment, Equity Ownership. Newland:GSK: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Baxter: Honoraria, Research Funding; Amgen: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Provan:GSK: Equity Ownership, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Baxter: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding, Speakers Bureau.

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