Increase in platelet–large cell ratio in chronic myeloid leukemia

Abstract

Thrombocytosis is defined as a platelet count of more than 400×10/l [1]. Differential diagnosis of thrombocytosis is not always obvious. Recently, automated hematological analysis has been common, and various parameters of blood cells can be used. However, there are many parameters whose significance are still unknown. Platelet–large cell ratio (P–LCR) is one of them, and is defined as the ratio of large platelets to total platelets, and is routinely performed by the automated hematological analyzer Sysmex NE-8000 (Sysmex, Kobe, Japan). In this parameter, a large platelet is defined as a platelet with a volume of 12 fl or more [2]. In this study, we examined the clinical usefulness of P–LCR in the differential diagnosis of thrombocytosis. The subjects studied were 50 patients with reactive thrombocytosis (RT), 30 patients with chronic myeloid leukemia (CML) (chronic phase), 15 patients with essential thrombocythemia (ET), and 5 patients with polycythemia vera (PV). P–LCR was higher in patients with CML (27.7 7.9 [mean S.D.]%; P 0.001), patients with ET (17.7 3.6%; P 0.002), and patients with PV (20.8 2.8%; P 0.005) than in patients with RT (13.4 4.1%) (Fig. 1). These findings are compatible with those of previous reports in which the number of large platelets increased in chronic myeloproliferative disorders, but not in RT [3,4]. Furthermore, the P– LCR was higher in patients with CML than in patients with RT (P 0.001), ET (P 0.001) or PV (P 0.001). When the mean+3 S.D. of the P–LCR in 50 patients with RT was determined as the ‘cut-off’ value for differential diagnosis of thrombocytosis between RT and CML, half of the P–LCRs (15/30) were above the ‘cut-off’ value in patients with CML. All of the P– LCRs were under the ‘cut-off’ in patients with RT, ET, or PV. Therefore, these data indicate the ‘cut-off’ value, which is the mean+3 S.D. of the P–LCR in RT patients is useful for the screening of CML in thrombocytosis.