Platelet count

Platelets are membrane encapsulated fragments of megakaryoctes. Although platelets have no nucleus, they are metabolically active and are able to express membrane receptors and release stored substances when triggered. However, because they have no nucleus they are unable to produce new proteins and therefore asprin and other drug effect function for the remainder of the platelet lifespan. Platelet lifespan is about 9-10 days.

Platelets function by adhering to the walls of injured blood vessels. They clump together or aggregate to form platelet plugs necessary for coagulation. Platelets are produced in the bone marrow and removed by the spleen when they are damaged or old. A normal platelet count ranges between 150,000 and 350,000. Platelet counts under 50,000 put a patient at risk of severe bleeding and platelet counts under 20,000 may cause spontaneous and fatal intracranial bleeding.

An increased platelet count is known as thrombocytosis. Patients who have an unexpectedly high platelet count may have an advanced or metastatic malignancy. A splenectomy also causes a temporary increase in the platelet count. Patients who have a high platelet count may have an increased risk of forming a thrombus. Importantly, a high platelet count may also place a patient at risk for a bleeding episode. When the platelet count is high, some of the platelets may be abnormal forms that do not function correctly to assist in the coagulation process.

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When a patient has a high platelet count, he or she is not at risk of bleeding.

A low platelet count is known as thrombocytopenia. Thrombocytopenia occurs with viral infections, AIDS, and as a consequence of bone marrow suppression, such as occurs with radiation therapy or chemotherapy. Extracorporeal bypass or autotransfusion also produce thrombocytopenia. Idiopathic thrombocytopenic purpura, a condition associated with easy bruising, refers to thrombocytopenia of unknown causation. Heparin therapy causes a decrease in the platelet count, therefore platelet counts should be assessed when a patient is receiving heparin.

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