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تاريخ التسجيل : 25/02/2010
 |  موضوع: الصفائح الدموية Platelet Count Tests  الثلاثاء 24 مايو - 21:37:49 | |
| Platelets, also called thrombocytes, are the smallest cells in the blood. These cells do not have a nucleus, are round or oval, flattened, disk-shaped structures, and are necessary for coagulation . Some texts refer to platelets as fragments of cytoplasm .
Two tests that measure or count the number of platelets are the platelet count, which measures the number of platelets in the blood, and the mean platelet volume (MPV), which provides information about platelet size.Platelet CountA platelet count test often follows a decreased platelet count that was estimated from a peripheral blood smear. The platelet count is an important blood test because thrombocytopenia is the most common cause of bleeding diseases. This count is used to evaluate bleeding disorders due to liver disease, thrombocytopenia, and anticoagulant therapy. The test is also ordered for patients who have diseases associated with bone marrow problems, such as leukemia and aplastic anemia. The platelet count is expressed as the number of platelets per cubic millimeter (mm3) of blood .Normal RangePlatelets 150,000-400,000/mm3Variations from Normal. An abnormal increase in the number of platelets is called thrombocythemia or thrombocytosis. This increase is seen in diseases such as malignancies, early stages of chronic granulocytic leukemia, polycythemia vera, tuberculosis, chronic inflammatory disease, and chronic blood loss.A decreased platelet count is known as thrombocytopenia and can result in significant bleeding problems. Diseases that decrease the platelet count include pernicious and aplastic anemias, and idiopathic thrombocytopenic purpura (ITP). A low platelet count is commonly seen in AIDS cases. Exposure to various chemicals and the toxic effects of many drugs can also lead to thrombocytopenia . Individuals whohave serious platelet deficits often show signs or symptoms such as petechiae, bleeding from gums, nosebleeds, and gastrointestinal bleeding.Interfering Circumstances . Platelet counts can show a normal increase at high altitudes, after strenuous exercise, and in the winter . A normal decrease occurs on the first day of an infant's life and before menstruation.Mean Platelet Volume (MPV)The mean platelet volume provides information about the relative size of platelets, which is calculated by a cell analyzer and compared to what is observed on a microscope slide. The diameter of the platelet is expressed in micrometers (!gym) . The MPV is a useful diagnostic tool for thrombocytopenic disorders.The relative size of platelets varies with platelet production. When theoverall platelet count drops, functioning bone marrow produces younger and larger platelets to compensate for the decreased number of platelets.This process results in an increased mean platelet volume . Lack of bone marrow function results in the decreased production of platelets, a diminished platelet size, and a decreased mean platelet volume.Normal RangePlatelets2-4 gm in diameterVariations from Normal. An increase in the diameter of the platelets occurs in systemic lupus erythematosus, idiopathic thrombocytopenic purpura in remission, various anemias, myeloproliferative disorders, and a variety of chronic disease processes. A decrease in the size of platelets is associated with aplastic anemia, megaloblastic anemia, and hypersplenism | |
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