Platelets, or thrombocytes, are the smallest formed elements in blood. They promote coagulation and the formation of a hemostatic plug in vascular injury.Platelet count is one of the most important screening tests of platelet function. Accurate counts are vital
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Normal platelet counts range from 140,000 to 400,000/u1.
A decreased platelet count (thrombocytopenia) can result from aplastic or hypoplastic bone marrow; infiltrative bone marrow disease, such as carcinoma, leukemia, or disseminated infection; megakaryocytic hypoplasia; in effective thrombopoiesis due to folic acid or vitamin B12 deficiency; pooling of platelets in an enlarged spleen; increased platelet destruction due to drugs or immune disorders; disseminated intravascular coagulation; Bernard-Soulier syndrome; or mechanical injury to platelets.
A platelet count that falls below 50,000/u1 can cause spontaneous bleeding. When it drops below 5,000, fatal central nervous system bleeding or massive GI hemorrhage is possible.
An increased platelet count (thrombocytosis) can result from hemorrhage, infectious disorders, malignant disease, iron deficiency anemia, recent surgery, pregnancy, splenectomy, or inflammatory disorders such as collagen vascular disease. In such cases, the platelet count returns to normal after the patient recovers from the primary disorder. However, the count remains elevated in primary thrombocythemia, myelofibrosis with myeloid metaplasia, polycythemia vera, and chronic myelogenous leukemia.
When the platelet count is abnormal, diagnosis usually requires further studies, such as complete blood count, bone marrow biopsy, direct antiglobulin test (direct Coombs' test), and serum protein electrophoresis.
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