Plateletpheresis

Plateletpheresis (more accurately called thrombocytapheresis or thrombapheresis, though these names are rarely used) is the process of collecting thrombocytes, more commonly called platelets, a component of blood involved in blood clotting. The term specifically refers to the method of collecting the platelets, which is performed by a device used in blood donation that separates the platelets and returns other portions of the blood to the donor. Platelet transfusion can be a life-saving procedure in preventing or treating serious complications from bleeding and hemorrhage in patients who have disorders manifesting as thrombocytopenia (low platelet count) or platelet dysfunction. This process may also be used therapeutically to treat disorders resulting in extraordinarily high platelet counts such as essential thrombocytosis. Plateletpheresis (more accurately called thrombocytapheresis or thrombapheresis, though these names are rarely used) is the process of collecting thrombocytes, more commonly called platelets, a component of blood involved in blood clotting. The term specifically refers to the method of collecting the platelets, which is performed by a device used in blood donation that separates the platelets and returns other portions of the blood to the donor. Platelet transfusion can be a life-saving procedure in preventing or treating serious complications from bleeding and hemorrhage in patients who have disorders manifesting as thrombocytopenia (low platelet count) or platelet dysfunction. This process may also be used therapeutically to treat disorders resulting in extraordinarily high platelet counts such as essential thrombocytosis. Platelet transfusions are traditionally given to those undergoing chemotherapy for leukemia, multiple myeloma, those with aplastic anemia, AIDS, hypersplenism, ITP, sepsis, bone marrow transplant, radiation treatment, organ transplant or surgeries such as cardiopulmonary bypass. Platelet transfusions should be avoided in those with TTP because it can worsen neurologic symptoms and acute renal failure, presumably due to creation of new thrombi as the platelets are consumed. It should also be avoided in those with heparin-induced thrombocytopenia (HIT) or disseminated intravascular coagulation (DIC). In adults, platelets are recommended in those who have levels less than 10,000/ul, less than 20,000/ul if a central venous catheter is being placed, or less than 50,000/ul if a lumbar puncture or major surgery is required. Not all platelet transfusions use platelets collected by automated apheresis. The platelets can also be separated from donations of whole blood collected in a traditional blood donation, but there are several advantages to separating the platelets at the time of collection. The first advantage is that the whole-blood platelets, sometimes called 'random' platelets, from a single donation are not numerous enough for a dose to give to an adult patient. They must be pooled from several donors to create a single transfusion, and this complicates processing and increases the risk of diseases that can be spread in transfused blood, such as human immunodeficiency virus. Collecting the platelets from a single donor also simplifies human leukocyte antigen (HLA) matching, which improves the chance of a successful transfusion. Since it is time-consuming to find even a single compatible donor for HLA-matched transfusions, being able to collect a full dose from a single donor is much more practical than finding multiple compatible donors. Plateletpheresis products are also easier to test for bacterial contamination, a leading cause of transfusion-associated deaths. Pooling of whole blood platelets is often done in an 'open' system where the platelet containers are connected in a way that could expose the platelets to air, and pooled platelets must be transfused promptly so that any contamination does not have time to grow. Problems with apheresis include the expense of the equipment used for collection. Whole blood platelets also do not require any additional donor recruitment, as they can be made from blood donations that are also used for packed red blood cells and plasma components. Recipients in this category include those undergoing chemotherapy, those with myelophthisic anemia, AIDS, or with aplastic anemia. If indicated, transfusions (one thrombapheresis concentrate) should be given until recovery of platelet function, generally approximately twice weekly. Surgical bleeding due solely to thrombocytopenia occurs when platelets < 50,000/µL while spontaneous bleeding occurs when platelets < 10,000/µL. Thrombocytopenic patients can develop 'dry' bleeding, that is, petechiae and ecchymoses only. They will not suffer fatal hemorrhagic events unless they first have extensive mucosal bleeding, or 'wet' bleeding. Therefore, in those with no bleeding or only 'dry' bleeding, the threshold for transfusion should be between 5,000 and 10,000/µL. A more conservative threshold of 20,000/µL should be used in those with a fever or other risk factors for bleeding. Those with active bleeding or prior to surgery should have a threshold of 50,000/µL. An unconfirmed, but helpful, way to determine whether a patient is recovering from chemotherapy-induced thrombocytopenia is to measure 'reticulated' platelets, or young RNA-containing platelets, which signifies that the patient is starting to make new platelets. Recipients in this category include those with ITP or drug-induced thrombocytopenia. Platelet transfusions are generally not recommended for this group of patients because the underlying cause involves antibodies that destroy platelets, therefore any newly transfused platelets will also be destroyed. Platelets transfusions may be used in emergency bleeding situations where the platelets could be used by the body before the immune system destroys them. More studies need to be done.