Response to meta-analysis of leukocytosis and thrombosis in essential thrombocythemia and polycythemia vera

We appreciated the recent meta-analysis by Carobbio et al published in the 7 June 2019 issue of Blood Advances entitled "Leukocytosis and thrombosis in essential thrombocythemia and polycythemia vera: a systematic review and meta-analysis." 1 The question of leukocytosis and the associated risk of thrombosis is one of vital clinical importance in patients with polycythemia vera (PV) and essential thrombocythemia (ET) because the answers are critical in developing improved risk-stratification tools for guiding management and informing the use of cytoreductive therapy, particularly in patients with persistent leukocytosis who are otherwise low risk by conventional scoring systems.Although we commend the authors' attempt to systematically answer this question using meta-analytic techniques, we would like to highlight some methodologic limitations of their approach.