SWISS MEDICAL WEEKLY: PLATELET TRANSFUSION

Platelet transfusion: basic aspects Nowadays platelet transfusions are an essential part of the supportive care of thrombocytopenic ­patients. The number of platelet transfusions continues to grow as a result of the increasing number of patients treated for haemato-oncological diseases, and of extension of the indications for platelet transfusions to include, for example, drug-related platelet dysfunction. This review focuses on current platelet component production and storage techniques, indications for platelet transfusion, and safety issues such as alloimmunisation and management of refractory platelet transfusion. Abstract In the 1950s, platelet transfusions were found to prevent major haemorrhage and improve survival in thrombocytopenic patients. Since then, their use has grown and continues to grow: nowadays, more than ­4 million platelet components are transfused worldwide each year. However, a number of questions have arisen related to the optimal preparation and storage of platelet components, and the indications for, and the safety and efficacy of, platelet transfusions. Platelet components can be obtained either from whole blood donations or by single donor apheresis. Both techniques have advantages and disadvantages. Platelet components derived from whole blood donations are produced by pooling either platelet rich plasma or buffy coats from multiple donors, using different sequential centrifugation steps. For the production of single donor apheresis platelet concentrates, donor availability is a major limitation of this process. Although specific ­adverse effects of platelet apheresis are well recognised, the process is considered safe and can even be safely performed in donors with mild anaemia and low iron stores. Platelet components are stored at 22 ± 2 °C under gentle agitation. Because possibly contaminating bacteria can grow well under these conditions, duration of storage is limited to 4–7 days, depending on whether bacterial ­detection methods or pathogen reduction are used. Various pathogen reduction techniques have been developed in recent years. One such technique, now mandatory in Switzerland, involves amotosalen, a psoralen ­derivative which binds to nucleic acids and, upon activation with ultraviolet-A, crosslinks them. An absorbing device then removes residual amotosalen (figure). Platelets can be transfused in order to prevent bleeding (prophylactic transfusion) or to stop bleeding (therapeutic transfusion) both in thrombocytopenic patients and in patients with normal platelet counts. The vast majority of recipients of platelet transfusions are thrombocytopenic patients with haemato-oncological diseases. Drug-induced platelet dysfunction is another indication for platelet transfusion. Assessment of the efficacy of platelet transfusion is very important and a major challenge. Several criteria have been developed and evaluated; most of them ­include the post-transfusion platelet count. Various factors have a direct or indirect influence on the efficacy of platelet transfusions. These can be product-related and patient-related, immune and nonimmune. Bleeding, infection/sepsis, splenomegaly and graft-­versus-host disease are the most common nonimmune causes for refractoriness to platelet transfusions. Drugs are also important causes of refractoriness. Immune factors are responsible for platelet transfusion refractoriness in approximately 20% of cases, with human ­leucocyte antigen (HLA) antibodies being most commonly involved. Platelet transfusions can be associated with various transfusion reactions, including, among others, febrile transfusion reactions (the most frequent), allergic reactions (generally mild), haemolysis due to donor iso­haemagglutinins and the risk of microbial contamination, which can lead to fatal sepsis. Alloimmunisation can be a problem in patients receiving multiple transfusions. It is related to residual red blood cells and leucocytes in the platelet components, as well as platelet ­antigens. Studies on alternatives to platelet transfusions and other methods to improve haemostasis in bleeding ­patients are under investigation. Development of platelets from haematopoietic stem cells, human embryonic stem cells and human induced pluripotent stem cells and expansion of ex-vivo generated platelets are further exciting fields of research. This is a summary of a paper that was published on www.smw.ch. Must be cited as: Holbro A, Infanti L, Sigle J, Buser A. Platelet transfusion: basic aspects. Swiss Med Wkly. 2013;143:w13885. - See more at: http://blog.smw.ch/platelet-transfusion-basic-aspects/#sthash.8Ndl4ZQ2.dpuf