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.