Measurement of reticulated platelets by simple flow cytometry: An indirect thrombocytopoietic marker

BACKGROUND: The aim of this study was to determine whether measurement of reticulated platelets (RP) by flow cytometry directly from whole blood, with no fixation or manipulation, is as useful a thrombocytopoietic marker as other more complex techniques. METHODS: RP percentage was prospectively assessed in thrombocytopenic patients (platelets <100x10(9)/L) and non-thrombocytopenic controls using a direct, whole-blood, dual-labelling flow cytometric method. Direct, whole-blood double coverage was achieved using a monoclonal antiglycoprotein (GP)-III antibody (CD61-PerCP(R)) for platelet identification and thiazol orange (Retic-count(R)) as platelet mARN stain. After establishing thrombocytopenia etiology, patients were grouped according to whether their rate of thrombopoiesis was increased or decreased. RESULTS: RP were measured in 53 thrombocytopenic patients with several etiologies and in 53 non-thrombocytopenic controls. The mean RP in 14 thrombocytopenic patients with no increased thrombopoietic activity was 4.8% (95% CI: 3.2-6.4) and the RP absolute number was 1.98x10(9)/L (95% CI: 1.3-2.6). The mean RP in 17 thrombocytopenic patients with increased thrombopoietic activity was 29.4% (95% CI: 24.7-34.1) and the RP absolute number was 7.24x10(9)/L (95% CI: 4.9-9.5). CONCLUSIONS: RP measurement by flow cytometry, directly from whole blood without manipulation, is a useful screening test to differentiate thrombocytopenia with high or low thrombopoietic activity.