Prediction of thrombotic and hemorrhagic events during polycythemia vera or essential thrombocythemia based on leukocyte burden

- In PV and ET, risk of thrombosis/hemorrhage is correlated with leukocyte burden.
- The event risk is especially higher when the leukocyte burden is > 11,000 × 103 μL.
- The leukocyte burden is higher immediately before thrombotic/hemorrhagic events.
- Controlling leukocytosis may decrease thrombosis/hemorrhage in PV/ET.

BackgroundEvidences suggest an association between leukocytosis and thrombotic or hemorrhagic complication in polycythemia vera (PV) and essential thrombocythemia (ET), but clinical implication is not well known.ObjectiveTo evaluate whether leukocyte burden during follow-up is related to thrombotic or hemorrhagic events in PV and ET.Patients/MethodsWe retrospectively analyzed patients with PV or ET treated at Seoul National University Bundang Hospital, Korea. Time-weighted averages of leukocytes during the follow-up period were defined as leukocyte burden and were calculated for each patient and compared between patient subgroups. In each patient with events, leukocyte burden for the 3-month period before the event was compared with that for the entire follow-up period.ResultsIn 102 patients with PV or ET, 35 events (16 thrombotic, 19 hemorrhagic) occurred in 29 patients (median follow-up, 54 months). Leukocyte burden were significantly higher in patients with events than in event-free patients (12,015 × 103 /μL vs. 9,567 × 103/μL, P = 0.003). The difference was more prominent in ET patients than in PV patients, and in patients with hemorrhagic events than in those with thrombotic events. In patients with events, the leukocyte burden in the pre-event period was higher than in the entire follow-up period (16,767 × 103/μL vs. 12,015 × 103/μL, P = 0.002). In all patients, leukocyte burden during entire follow-up period of 11,000 × 103/μL or higher was an independent risk factor for vascular events.ConclusionIn PV or ET patients, leukocyte burden during disease course is related to increased incidence of thrombotic or hemorrhagic events.