Neither enduring leukocytosis nor persistently elevated hematocrit levels were found to be markers of thrombosis in the setting of polycythemia vera (PV). These findings of a large retrospective study were published in Blood.

The main purpose of this study was to address the question of whether persistent leukocytosis occurring in patients with PV, a chronic Philadelphia chromosome-negative myeloproliferative neoplasm (MPN) most notably characterized by erythrocytosis, is associated with an increased risk of thrombosis and/or disease progression.

Through an analysis of longitudinal hematologic laboratory data collected at 3-month intervals (whenever possible) from 10 academic institutions in the United States, models were developed to separately cluster the hematologic trajectories of  leukocyte counts, platelet counts, and hematocrit levels of 440/520 patients with PV into separate trajectory groups.

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Inclusion in a trajectory group was then evaluated for associations with risks for 2 major outcomes, thrombosis and disease progression to myelofibrosis, myelodysplastic syndrome, or acute myeloid leukemia, for 377 and 378 patients, respectively, with a median follow-up of 48 months for both evaluations. The analyses only included patients with 3 or more sets of hematologic laboratory data collected over a 12-month period following an index date corresponding to the first set of laboratory values who did not experience either a thrombotic event or disease progression during the 12-month landmark period.

In this patient cohort, 4 leukocyte, 3 platelet, and 3 hematocrit distinct trajectory groups were identified.

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Following adjustment for multiple covariates using multivariable analysis, no significant associations were observed between leukocyte (P =.4164), hematocrit (P =.1849), or platelet trajectory group (P =.9501) and the likelihood of experiencing a thrombotic event. Also observed was that inclusion in a given hematocrit (P =.5407) or platelet trajectory group (P =.1670) was not associated with risk of progression of PV. However, the presence of persistent leukocytosis was associated with “an increased hazard of disease evolution in an ascending stepwise manner (overall P =.0002),” the study authors reported.

“Prospective trial of leukocyte control in otherwise uncontrolled patients with a primary endpoint of disease evolution may therefore be warranted,” the study authors noted in their concluding remarks.


Ronner L, Podoltsev N, Gotlib J, et al. Persistent leukocytosis in polycythemia vera is associated with disease evolution but not thrombosis [published online February 27, 2020]. Blood. doi:10.1182/blood.2019003347