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Thrombocytopenia
(Low Platelet Count)

Medical Author: Siamak Nabili, MD, MPH
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

What is thrombocytopenia?

Thrombocytopenia is a lower than normal number of platelets in the blood.

Platelets are one of the components of the blood along with white and red blood cells. Platelets play an important role in clotting and bleeding. Platelets are made in the bone marrow similar to other cells in the blood such as, white blood cells and red blood cells. Platelets originate from megakaryocytes which are large cells found in the bone marrow. The fragments of these megakaryocytes are platelets that are released into the blood stream. The circulating platelets make up about two third of the platelets that are released from the bone marrow. The other one third is typically stored (sequestered) in the spleen.

Platelets, in general, have a brief 7 to 10 days life in the blood, after which they are removed from the blood circulation. The number of platelets in the blood is referred to as the platelet count and is normally between 150,000 to 450,000 per micro liter (one millionth of a liter) of blood. Platelet counts less than 150,000 are termed thrombocytopenia. Platelet counts greater that 450,000 are called thrombocytosis.

The function of platelets is very important in the clotting system. Platelets are a part of a very complicated pathway. They circulate in the blood vessels and become activated if there is any bleeding or injury in the body. Certain chemicals are released from the injured blood vessels or other structures that signal platelets to become activated and join the other components of the system to stop the bleeding. When activated, the platelets become sticky and adhere to one another and to the blood vessel wall at the site of the injury to slow down and stop the bleeding by plugging up the damaged blood vessel or tissue (hemostasis).

It is important to note that, even though, the platelet numbers are decreased in thrombocytopenia, their function usually remains completely intact. Other disorders exist that can cause impaired platelet function despite normal platelet count.

Low platelet count in severe cases may result in spontaneous bleeding or may cause delay in the normal process of clotting. In mild thrombocytopenia, there may be no adverse effects in the clotting or bleeding pathways.

Picture of platelets and a blood clot
Picture of platelets and a blood clot



Next: What causes thrombocytopenia? »

Thrombocytopenia

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Thrombocytopenia (Low Platelet Count)

What is a hematoma?

By definition, a hematoma is a collection of blood outside of a blood vessel. It occurs because the wall of a blood vessel wall, artery, vein or capillary, has been damaged and blood has leaked into tissues where it does not belong. The hematoma may be tiny, with just a dot of blood or it can be large and cause significant swelling.

The blood vessels in the body are under constant repair. Minor injuries occur routinely and the body is usually able to repair the damaged vessel wall by activating the blood clotting cascade and forming fibrin patches. Sometimes the repair fails if the damage is extensive and the large defect allows for continued bleeding. As well, if there is great pressure within the blood vessel, for example a major artery, the blood will continue to leak and the hematoma will expand.

Blood that escapes from the blood stream is very irritating and may cause symptoms of inflammation including pain, ...

Read the Hematoma article »










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