Immature Platelet Fraction as a Potential Biomarker of Dysregulated Thrombopoiesis in Philadelphia-Negative Myeloproliferative Neoplasms

<b>Background/Objectives</b>: Thrombotic events represent the leading cause of morbidity and mortality in patients with Philadelphia chromosome-negative myeloproliferative neoplasms (Ph^- MPNs), particularly in those aged > 60 years. The immature platelet fraction (IPF) reflects the proportion of newly released, reticulated, highly reactive platelets and has emerged as a marker of thrombopoietic activity in various prothrombotic conditions. <b>Methods</b>: We prospectively measured IPF in 45 patients with newly diagnosed Ph^- MPNs (24 with essential thrombocythemia, 13 with polycythemia vera, 5 with MPN-unclassified, and 3 with primary myelofibrosis) and 27 controls without MPN. <b>Results</b>: IPF was significantly higher in patients with Ph^- MPN than in controls (median 27 vs. 10.9, <i>p</i> < 0.0001). Within the MPN cohort, IPF values differed significantly across subtypes (<i>p</i> = 0.027), being highest in essential thrombocythemia and primary myelofibrosis, intermediate in unclassified MPN, and lowest in polycythemia vera. Patients older than 60 years exhibited higher IPF independently of platelet count (<i>p</i> = 0.021). No significant difference was observed between JAK2V617F-positive and -negative cases. <b>Conclusions</b>: These results indicate that IPF captures accelerated and dysregulated thrombopoiesis characteristics of Ph^- MPNs and may provide additional insight into subtype-specific biology and age-related prothrombotic risk beyond conventional complete blood count parameters.