Reticulated platelets as a screening test to identify thrombocytopenia aetiology

Background: Thrombocytopenia is a common haematological abnormality and no simple diagnostic test is available to diagnose thrombocytopenia pathogenesis. Aim: To evaluate sensitivity and specificity of reticulated platelets (RP) as a diagnostic test for thrombocytopenia with increased thrombopoietic activity. Design: Prospective observational study in thrombocytopenic patients. Methods: A direct, whole-blood, dual-labelling flow cytometric method was used. Direct, whole-blood double coverage was achieved using a monoclonal anti-glycoprotein (GP)-III antibody (CD61 PerCP) for platelet identification and thiazole orange (Retic-count) as platelet mARN stain. Results: RP were measured in 101 thrombocytopenic patients and 104 non-thrombocytopenic controls. The mean RP percentage in 60 thrombocytopenic patients with no increased thrombopoietic activity was 7.5 (CI for 95: 5.2-9.7) and RP absolute number was 3.2 x 10(9)/l (CI for 95: 2.1-4.3). The mean RP percentage in 41 thrombocytopenic patients with increased thrombopoietic activity was 30.3 (CI for 95: 25.1-35.5) and RP absolute number was 6.2 (CI for 95: 4.8-7.7). The RP percentage cut-off for a diagnosis of thrombocytopenia with increased thrombopoietic activity was 11 [sensitivity 93, specificity 85, positive predictive value (PPV) 83, negative predictive value (NPV) 95]. Conclusions: RP measurement by flow cytometry, directly from whole-blood, is a useful screening test to differentiate between thrombocytopenia with high or low thrombopoietic activity. A RP percentage in excess of 11, has a high sensitivity and good specificity for a diagnosis of thrombocytopenia with increased thrombopoietic activity.