Extreme thrombocytosis: what are the etiologies?

Increase platelet count or thrombocytosis, defined as a platelet count greater than or equal to 350 x 10(9)/L, is a common hematologic aberration seen in complete blood cell count. Several etiologies are documented for thrombocytosis. Extreme thrombocytosis, defined as a platelet count greater than or equal to 1,000 x 10(9)/L, is rarely seen in general practice. There are limited data on the etiology of this abnormality. Here, a retrospective investigation for the etiology of severe thrombocytosis was performed. Of the 3 included reports, 535 cases with extreme thrombocytosis were investigated for their etiologies. The 2 defined etiologies are secondary thrombocytosis (66.6%) and clonal thrombocytosis. Of those cases with clonal thrombocytosis, 93.8% had myeloproliferative disorders, and 6.2% had essential thrombocytosis. Concerning bleeding and vaso-occlusive complications, all cases had these complications. In this study, 7.9% of the cases with secondary thrombocytosis experienced bleeding and vaso-occlusive complications, while 17.1% of the cases with clonal thrombocytosis did.