REVEAL: Elevated WBC count and thrombotic events in PV

Between 34% and 41% of patients with polycythemia vera (PV) experience thrombotic events (TE). Established risk factors for TE include JAK2 mutation, advanced age, TE history, and elevated hematocrit.¹ In addition, retrospective studies have shown elevated white blood cell (WBC) count to be associated with increased TE risk.¹ Here, we summarize a prospective, observational study by Gerds et al.¹ published in Blood which investigated association between WBC count and TE in patients with PV enrolled in the REVEAL study.¹

REVEAL study design

• REVEAL (NCT02252159) investigated patients ≥18 years with PV with a history of, or a plan to undergo, allogeneic stem cell transplant (allo-HCT) within 3 months of enrollment.
• Data were collected for 6 months across centers in the US, from July 2014 to August 2016.
  • Median follow-up was 44.7 months.
• A covariate Cox proportional hazards model was used to assess the association between WBC count and TE occurrence.

Key findings

• Overall, 2,271 patients with PV were included.
  • Median age was 67 years, and 54.1% of patients were male.
  • More patients were classed as high risk than low risk (77.9% vs 22.1%).
  • Median disease duration from diagnosis was 4.1 years, and 20.1% of patients had a history of TE.
• Within the population analyzed, 4.7% experienced TEs at an incidence of 1.36/100 patient-years, and most experienced one event compared with two to five events (81.1% vs 18.9%, respectively).
  • The cumulative incidence of venous TEs was higher than arterial TEs (3.13% vs 1.54%).
  • The cumulative incidence of TEs occurring in patients classed as high risk was higher than patients classed as low risk (5.2% vs 2.78%).
• TE occurrence was significantly associated with elevated blood counts (Table 1).

Table 1. REVEAL: Blood counts and associated TE risk* 

HCT, hematocrit level; HR, hazard ratio; NEUT, absolute neutrophil count; NS, not significant; PLT, platelet; TE, thrombotic event; WBC, white blood cell count.

*Adapted from Gerds, et al.¹

^†Association significance was not sustained a year after initial assessment.

• When comparing high-risk vs low-risk, WBC was associated with increased risk of TE in both subgroups and was the only association found in patients with low risk.
  • In high-risk patients, male sex, HCT, and PLT were also associated with increased risk of TE.