Performance Evaluation of Automated Impedance and Optical Fluorescence Platelet Counts Compared With International Reference Method in Patients With Thalassemia

Abstract

Context.— Spurious platelet counts from automated methods have been reported in patients with abnormal red blood cells. However, there is no specific study regarding performance of platelet counts by automated methods in patients with thalassemia. Objective.— To investigate the performance of automated platelet counts, including impedance (PLT-I) and optical fluorescent (PLT-O and PLT-F) methods, and compare them with the international reference method (IRM) for platelet counting in patients with thalassemia. Design.— Two hundred forty-nine thalassemia specimens from various subtypes were examined. PLT-I, PLT-O, and PLT-F from a Sysmex XN analyzer were evaluated and compared against the IRM. Demographic data, platelet counts, and red blood cell parameters are shown. Comparability between evaluated methods and IRM, as well as test characteristics, is presented. Factors involving inaccurate PLT-I were analyzed. Results.— Specimens with platelet counts ranging from 31 × 103/μL to 932 × 103/μL were included. Most patients were patients with thalassemia major. Correlation between PLT-I and IRM was lower than that of the other methods in overall patients. PLT-O and PLT-F were correlated to IRM when classifying patients according to clinically significant platelet ranges. All automated methods had acceptable sensitivities; however, specificity of PLT-I was low for diagnosis of thrombocytopenia. High RDW-CV (red blood cell distribution width–coefficient of variation) was an independent factor of inaccurate PLT-I measurement. Conclusions.— Among the evaluated methods, PLT-I was the method least correlated to IRM, with PLT-O and PLT-F comparable to IRM in patients with thalassemia. Optical platelet counts and careful blood smear examination are recommended alternative platelet counting methods, depending on the clinical setting.