Essential thrombocythemia in patients with platelet counts below 600x109/L: Applicability of the 2008 World Health Organization diagnostic criteria revision proposal

Abstract

The World Health Organization (WHO) diagnostic criteria as well as the Polycythemia Vera Study Group (PVSG) criteria define platelet counts above 600x10 9 /L as the threshold for essential thrombocythemia (ET) diagnosis [1,2]. It has been argued that such threshold excludes a number of patients with actual ET with platelet counts below 600 x 10 9 /L [3-5]. Recently, a proposal for revision of the WHO diagnostic criteria for ET has been published, which includes the combination of histological bone marrow study and testing of the JAK2 mutation to facilitate the diagnosis of ET with borderline thrombocytosis [6,7]. The aim of this study was to evaluate the applicability of the proposal of the WHO revised diagnostic criteria in patients presumed to have ET with platelet counts below 600 x 10 9 /L. Additionally, clinical and laboratory features of this group were compared to the group with platelet counts above 600 x 10 9 /L to assess any differences between both groups. Finally, clinical and laboratory features of JAK2 positive patients were compared to JAK2 negative patients to confirm in our series the differences previously described in the literature [8,9].