New trends in platelet transfusion

platelets or thrombocytes, the smallest of blood cellular elements, are the cell fragments of megakaryocytes circulating in the blood. They have a critical role in the cellular mechanisms of primary hemostasis leading to the formation of blood clots. Dysfunction or low levels of platelets predisposes to bleeding, while high levels, although usually asymptomatic, may increase the risk of thrombosis. There are two main indications for platelet transfusions: therapeutic and prophylactic. Platelet transfusions are considered therapeutic if they are given to control active bleeding whether due to thrombocytopenia and/or platelet dysfunction. All the other indications are more or less relative and depend on the clinical condition of the patient. Plateletpheresis is the process of collecting platelets, the components of blood that are involved in hemostasis. It can be a life-saving procedure in preventing or treating serious complications from bleeding and hemorrhage in patients who have disorders manifesting as thrombocytopenia or platelet dysfunction. This process may also be used therapeutically to treat disorders resulting in extraordinary high platelet counts such as essential thrombocytosis. Platelets for transfusion are provided as platelet concentrates, of which two preparations are currently available: single unit concentrates and platelet-pheresis concentrates. Platelets are stored at room temperature with constant agitation, which is necessary for the maintenance of platelet viability. PCs have until recently been stored for a maximum of five days due to the risk of bacterial growth. The introduction of bacterial detection systems and bacteria inactivation procedures has made it possible to extend the storage period up to 7 days provided the platelet function is well maintained. The magnitude of the changes would not result in the diminution of transfusion efficacy in a clinical situation. During storage, the platelets metabolize glucose to lactate and hydrogen, which is buffered by bicarbonate present in the plasma, resulting in a release of CO2. Platelet concentrates may be provided by the blood bank in their individual plastic bags or pooled before transfusion. Once the blood bag is opened by puncturing one of the sealed ports, the platelets must be administered within 4 hours. Platelets must be administered through a filter approved for platelet use, either a standard 170-μm filter or a leukoreduction platelet filter. Platelet transfusions should be avoided in those with thrombocytopenic purpura and hemolytic uremic syndrome because it can worsen neurological symptoms and acute renal failure, presumably due to creation of new thrombi as platelets are consumed. It should also be avoided in those with heparin-induced thrombocytopenia. The potential complications of platelet transfusion therapy are many, but most problems are present only in patients requiring repeated or large numbers of transfusions. Platelet transfusion complications can be classified as immunologic and non-immunologic. Many of immune reactions are caused by the stimulation of antibody production by foreign alloantigen present on transfused platelets. Platelet-transfusion refractoriness is a major complication ad usually refers to a condition where a patient fails to respond with expected increment to two to three consecutive transfusions. Patients are usually considered alloimmunized after two to three random donor transfusions with unsuccessful increment and concomitant detection of platelet alloantibodies.