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A Review Of The Use Of Platelets
Blood is circulated by the heart around the body and performs many physiological functions because of the many components in blood. Half of the blood consists of cells, whereas the other half is plasma fluid. Plasma contains the nutritional material, waste, and proteins which play a part in haemostasis as discussed later in the review. Erythrocytes are one of the cells in blood, they contain haemoglobin and their main function is to transport oxygen from the lungs to the body tissues. Blood also contains leukocytes and plays a role in defending the body from pathogens and foreign antigens. Finally the blood contains platelets, which are very small and work together with coagulation factors to play a major role in haemostasis.
In order to understand the use of platelets in transfusion their physiological function should be considered. Haemostasis is a normal physiological response that helps avoid excessive bleeding and haemorrhaging. They have other function such as making sure the blood is fluid and in motion thereby maintaining blood vessel integrity (Verhamme, 2009). Haemostasis is a response of three different stages that progress through time. The first response which is known as primary haemostasis and this is where the platelet cells in the blood are activated once they come into contact with the exposed endothelial cells, especially collagen due to the vascular damage. The final haemostasis response causes fibrinolysis to separate and dissolve the blood clot (Verstraeten, 2004).
Going back to primary haemostasis the platelets release a substance that causes the vascular muscles in the vessel to constrict, and expose a phospholipid structure that reacts with proteins known as a coagulation factors including fibrinogen and are found in the plasma. The damaged vessel releases a certain lipoprotein (tissue thromboplastin) that activates coagulation in the plasma forming a fibrin clot, which is the pus that is released once the clot is penetrated.
Use Of platelets
There are several uses of platelets for transfusion purposes that are available for a variety of patients.
Children with malignant diseases such as Acute Lymphoblastic Leukaemia (ALL) or Acute Myeloid Leukaemia (AML) are the most common type of patients that can receive transfusions. This technique is used to treat excessive bleeding and also when blood platelet levels fall drastically. If patients with ALL show symptoms of the disease or are bleeding continuously and prone to infections then prophylactic platelet transfusion therapy is used to raise the platelet count. In patients with AML platelet transfusions are carried out during induction chemotherapy and then later on again during stem cell transplantation. Higher threshold platelet count is required in patients suffering from disease-induced thrombocytopenia.
Transfusion in stem cell recipients is another use of platelets, particularly before the engraftment phase of transplantation. ABO incompatibility may be an issue with platelet transfusions and therefore the composition must be consistent with both the donor and recipient.
Children with congenital platelet disorders may also require transfusion. Inherited disorders such as Bernard-Soulier disease and Glanzmann's thrombasthenia may cause patients to bleed excessively during surgery or on other occasions. Apherisised platelets should be used.
Transfusions may also be required in patients who have abnormal platelets as a result of diseases such as Wiskott-Aldrich or Fanconi anaemia. However transfusions should be carried out prudently and reserved mainly for major bleeding episodes.
Platelet transfusion can also be used during pregnancy. Situations include excessive bleeding that can occur during the post-natal period, consumptive coagulopathy, placental breakage, and serious toxaemia or HELLP syndrome. Cytomegalovirus (CMV) status should be checked and if negative or unknown then CMV seronegative platelets should be administered.
CMV and other infections in the newborn, such as rubella and syphilis may result in repression of platelet production that can lead to enlargement of the spleen and also a decreased platelet lifespan. Platelet transfusion for neonatal congenital infections may therefore be a possibility.
Platelet alloimmunisation may cause foetal thrombocytopenia and therefore transfusion therapy into the uterus of the baby during pregnancy can be achievable to increase the platelet count. Intrauterine transfusions (IUT) are also used to avoid brain haemorrhages and other areas where excessive bleeding can occur. However IUTs are known to cause foetal death in approximately 1% of cases.
Patients involved in ECMO therapy or having a cardiopulmonary bypass can also have platelet transfusion therapy. Abnormally high levels of bleeding can be replaced to return platelet levels to somewhere near normality.
Infants with Foetomaternal Alloimmune Thrombocytopenia with or without Intra-cerebral haemorrhage can have transfusion to normalise or replace platelet loss, making sure also that platelet-specific antigen used is negative.
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Verstraeten, L et al. (2004). Journal de pharmacie de Belgique. The physiology of primary hemostasis. 44 (4), P302-307.
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HG Klein and DJ Anstee; Mollison's Blood Transfusion in Clinical Medicine Ch14 p611-612; ch15 p675.
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THE ROYAL CHILDREN'S HOSPITAL, MELBOURNE (2008) Platelet transfusion [WWW]. Available from: http://www.rch.org.au/bloodtrans/about.cfm?doc_id=7374 [Accessed 24/02/10].