SummaryA new automated method to reliably quantify reticulated platelets, expressed as the immature platelet fraction (IPF), has been developed utilizing the XE-2100 blood cell counter with upgraded software (Sysmex, Kobe, Japan). The IPF is identified by flow cytometry techniques and the use of a nucleic acid specific dye in the reticulocyte/optical platelet channel. The clinical utility of this parameter was established in the laboratory diagnosis of thrombocytopenia due to increased peripheral platelet destruction, particularly autoimmune thrombocytopenic purpura (AITP) and thrombotic thrombocytopenic purpura (TTP). Reproducibility and stability results over 48 h were good. An IPF reference range in healthy individuals was established as 1AE1-6AE1%, with a mean of 3AE4%. Patients in whom platelet destruction might be abnormal, were studied and two of these patients followed serially during the course of treatment. The IPF was raised in several disease states. The most significant increases in IPF values were found in patients with AITP (mean 22AE3%, range 9AE2-33AE1%) and acute TTP (mean 17AE2%, range 11AE2-30AE9%). Following patients during treatment demonstrated that as the platelet count recovered the IPF% fell. These results show that a rapid, inexpensive automated method for measuring the IPF% is feasible and should become a standard parameter in evaluating the thrombocytopenic patient.

SummaryAlthough haematology analysers provide reliable full blood counts, they are known to be inaccurate at enumerating platelets in severe thrombocytopenia. If the thresholds for platelet transfusion, currently set at 10 · 10 9 /l, are to be further reduced, it is vital that the limitations of current analysers are fully understood. The aim of this large multicentre study was to determine the accuracy of haematology analysers in current routine practice for platelet counts below 20 · 10 9 /l. Platelet counts estimated by analysers using optical, impedance and immunological methods were compared with the International Reference Method for platelet counting. The results demonstrated variation in platelet counting between different analysers and even the same type of analyser at different sites. Optical methods for platelet counting on the XE 2100, Advia 120, Cell-Dyn 4000 and H3* were not superior to impedance methods on the XE 2100, LH750 and Pentra analysers. All analysers except one overestimated the platelet count, which would result in under transfusion of platelets. This study highlights the inaccuracies of haematology analysers in platelet counting in severe thrombocytopenia. It re-emphasizes the need for external quality control to improve analyser calibration for samples with low platelet counts, and suggests that the optimal thresholds for prophylactic platelet transfusions should be re-evaluated.

summary. The decision to prophylactically transfuse platelets is dependent on the platelet count, careful regular clinical assessment and agreed local protocol. The ability to predict when platelet recovery will occur should allow a more reasoned approach to platelet transfusion. An increase in reticulated platelets demonstrates impending platelet recovery. A new rapid automated method to assess reticulated platelets, the immature platelet fraction (IPF), is described, and its clinical utility assessed. The IPF is identified by flow cytometry with the use of a nucleic acid specific dye in the reticulocyte channel on the Sysmex XE-2100. Fifty healthy adult volunteers were used to establish the normal range. Patients where platelet marrow production or destruction might be abnormal were studied, and some patients followed serially during treatment. Thirty patients receiving cytotoxic chemotherapy were tested, and 13 of these patients followed serially. Fifteen patients post-autologous or allogeneic transplant were followed daily for platelet count and IPF percentage to monitor platelet recovery. The method demonstrates good reproducibility and stability. The recovery phase of thrombocytopenia in most chemotherapy and transplant patients was preceded by a rise in IPF percentage several days prior to platelet recovery. In particular, patients undergoing autologous transplantation (n = 8) using peripherally collected stem cells have a characteristic IPF percentage motif, with a rise one or two days prior to engraftment. The automated IPF is a useful parameter in the clinical evaluation of the thrombocytopenic patient and has the potential to allow optimal transfusion of platelet concentrates.