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Information on the PLT Blood Test

written by: Leigh A. Zaykoski•edited by: Leigh A. Zaykoski•updated: 2/28/2010

The PLT blood test allows doctors to determine if abnormal platelet levels exist in the blood. Abnormal platelet levels indicate several medical problems, allowing doctors to make a diagnosis and provide patients with proper treatment.

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    Platelets help the blood clot properly, preventing clotting disorders such as excessive bleeding and increased risk for blood clots. The bone marrow produces these blood cell fragments and releases them into the blood. Platelets form as the result of the breakdown of megakaryocytes, large cells that exist in the bone marrow. One megakaryocyte forms over 1,000 platelets. A hormone called thrombopoietin controls the development of megakaryocytes and the eventual production of platelets. Platelets get their name from their plate-like shape.

    The structure of the platelet helps it carry out its blood clotting functions. Proteins on the platelet surface allow them to stick to each other and stick to vascular walls, stopping bleeding from injuries. They also contain granules that manufacture proteins used to seal breaks in the blood vessels.

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    The PLT Blood Test

    The platelet blood test is a simple count of the number of platelets in the blood. A normal platelet count ranges from 150,000 to 400,000 platelets in one microliter of blood. A lab tech does the count on a sample of blood drawn from a vein in the arm, making this test quick and safe to complete. The lab reports platelet test results to the ordering physician, and the physician informs the patient about any abnormalities.

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    Too Many Platelets

    When a person’s platelet count is high, there is an increased risk for blood clots and other serious clotting disorders. A doctor may order a blood thinner (anticoagulant) to prevent strokes and pulmonary embolisms caused by blood clots.

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    Low Platelet Count

    When the platelet count is too low, it increases the risk for excessive bleeding. Low platelet count, also called thrombocytopenia, has several causes. If the bone marrow does not produce platelets normally, this leads to thrombocytopenia. Destruction of the platelets once they leave the bone marrow also results in a low platelet count. Some medications, such as chemotherapy drugs, destroy platelets, resulting in a low platelet count. Other drugs responsible for low platelet count include quinidine, acetaminophen, sulfa drugs, vancomycin, digoxin, nitroglycerine, and valium. Kidney and spleen disorders also cause premature destruction of the platelets.

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    Ordering the Test

    Lab techs often do the PLT blood test as part of the complete blood count, which also counts the numbers of red and white blood cells in the blood. Doctors also order the platelet blood test when someone exhibits signs of a clotting disorder. These signs include unexplained bruising and excessive bleeding that is difficult to control. The complete blood count also includes a test known as the MPV blood test, or mean platelet volume. The size of platelets varies based on their age, but an abnormal MPV test results can indicate a problem with platelet production, giving doctors additional information needed to make a diagnosis. The results of the complete blood count help doctors determine which other blood tests should be ordered.