Thrombocytopenia (THROM-bo-si-to-PE-ne-ah) is a condition in which your blood has a lower than normal number of blood cell fragments called platelets (PLATE-lets).
Platelets are made in your bone marrow along with other kinds of blood cells. They travel through your blood vessels and stick together (clot) to stop any bleeding that may happen if a blood vessel is damaged. Platelets also are called thrombocytes (THROM-bo-sites) because a clot also is called a thrombus.
When your blood has too few platelets, mild to serious bleeding can occur. Bleeding can occur inside your body (internal bleeding) or underneath your skin or from the surface of your skin (external bleeding).
A normal platelet count in adults ranges from 150,000 to 450,000 platelets per microliter of blood. A platelet count of less than 150,000 platelets per microliter is lower than normal. If your blood platelet count falls below normal, you have thrombocytopenia.
However, the risk for serious bleeding doesn't occur until the count becomes very low—less than 10,000 or 20,000 platelets per microliter. Mild bleeding sometimes occurs when the count is less than 50,000 platelets per microliter.
Many factors can cause a low platelet count, such as:
How long thrombocytopenia lasts depends on its cause. It can last from days to years.
The treatment for this condition also depends on its cause and severity. Mild thrombocytopenia often doesn't require treatment. If the condition causes or puts you at risk for serious bleeding, you may need medicines or blood or platelet transfusions. Rarely, the spleen may need to be removed.
Thrombocytopenia can be fatal, especially if the bleeding is severe or occurs in the brain. However, the overall outlook for people who have the condition is good, especially if the cause of the low platelet count is found and treated.
The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.