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Hematocrit (HCT) Levels and Thrombotic Events Among US Veterans With Polycythemia Vera

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Background: Thrombotic events (TEs) are a leading cause of death in patients with polycythemia vera (PV), contributing to lower overall survival compared with age/sex-matched controls. This analysis evaluated the relationship between HCT levels and TEs among patients with PV from the Veteran’s Health Administration (VHA) to replicate the findings of the Cytoreductive Therapy in Polycythemia Vera (CYTO-PV) trial with a real-world patient population.

Methods: This retrospective study used VHA medical record and claims data from first PV diagnosis claim (index) until death, disenrollment, or end of study (collected October 1, 2005, through September 30, 2012). Patients were aged ≥ 18 years at index, had ≥ 2 PV claims (ICD-9-CM code, 238.4) ≥ 30 days apart during the identification period, continuous health plan enrollment from 12 months pre-index until end of study, and ≥ 3 HCT measurements/year during follow-up. This analysis focused on patients with no pre-index TE and all HCT values either < 45% or ≥ 45% during follow-up. Patient demographics and disease characteristics were assessed using descriptive statistics. Associations between HCT levels and TE occurrence were analyzed using unadjusted Cox regression models for patients with ≥ 1 HCT before TE (≥ 1 HCT subgroup). A sensitivity analysis including patients with a history of TE before the index period was also performed.

Results: Patients (n=213) were mean (SD) age 68.9 (11.5) years and predominately white (61.5%). TE during follow-up occurred in 44.1% of patients (mean follow-up, 2.3 y; rate per 100 person-years, 18.9). The 3 most common types of TE were ischemic stroke (21.6%), deep vein thrombosis (12.2%), and transient ischemic attack (9.4%). TE rates for patients with HCT values 45% vs < 45% were 54.2% and 40.3%, respectively. In the 1 HCT subgroup (n=208), the TE risk hazard ratio was 1.61 (95% CI, 1.03–2.51; P=0.036). The sensitivity analysis, which included patients with and without pre-index TEs (n=342), had similar results (76.9% vs 55.6%); hazard ratio in the 1 HCT subgroup (n=322):, 1.95 (95% CI, 1.46–2.61; P<0.0001).

Implications: These results in agreement with CYTOPV study findings and further support effective monitoring and management of HCT levels < 45% to reduce the risk of TE in veterans with PV.

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