BACKGROUND

Evidences 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.

OBJECTIVE

To evaluate whether leukocyte burden during follow-up is related to thrombotic or hemorrhagic events in PV and ET.

PATIENTS/METHODS: We 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.

RESULTS

In 102 patients with PV or ET, 35 events (16 thrombotic, 19 hemorrhagic) occurred in 29 patients (median follow-up, 54months). Leukocyte burden were significantly higher in patients with events than in event-free patients (12,015×10(3) /μL vs. 9,567×10(3)/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 (16,767×10(3)/μL vs. 12,015×10(3)/μL, P=0.002). In all patients, leukocyte burden during entire follow-up period of 11,000×10(3)/μL or higher was an independent risk factor for vascular events.

CONCLUSION

In PV or ET patients, leukocyte burden during disease course is related to increased incidence of thrombotic or hemorrhagic events.