Key Points

• Thrombocythemia and thrombocytosis are conditions in which your blood has a high number of blood cell fragments called platelets. Platelets travel through your blood vessels and stick together (clot) to stop any bleeding that could happen if a blood vessel is damaged.
• The term "thrombocythemia" is preferred when the cause of the high platelet count isn't known. The condition is then called primary or essential thrombocythemia. In this condition, faulty stem cells in the bone marrow make too many platelets. In some cases, the condition is inherited or caused by a genetic mutation.
• When another disease or condition causes a high platelet count, the term "thrombocytosis" is preferred. This condition often is called secondary or reactive thrombocytosis. Secondary thrombocytosis is more common than primary thrombocythemia.
• Most people who have these conditions have no signs or symptoms. In those who do, the most common symptoms are linked to blood clots and bleeding. Symptoms include weakness, bleeding, headache, and numbness of the hands and feet.
• People who have primary thrombocythemia are more likely than those who have secondary thrombocytosis to have serious signs and symptoms.
• Thrombocythemia and thrombocytosis are diagnosed based on your medical history, a physical exam, and test results. Primary thrombocythemia is diagnosed only after all other possible causes of a high platelet count are ruled out.
• People who have primary thrombocythemia but no signs or symptoms don't need treatment, as long as the condition remains stable. Other people who have this form of the condition may need medicines or procedures to treat it.
• Secondary thrombocytosis is treated by addressing the underlying condition that's causing it.
• You can't prevent primary thrombocythemia. But, you can take steps to reduce your risk for blood clots and prevent related problems. Stop smoking and work to control your blood pressure and blood cholesterol.
• You can't always prevent conditions that lead to secondary thrombocytosis. However, if you have regular medical care, your doctor may find these conditions before you develop a high platelet count.
• If you have thrombocythemia or thrombocytosis, get regular medical care. Stop smoking and control risk factors for blood clots. Watch for signs and symptoms of blood clots and bleeding and report them to your doctor right away. Take all your medicines as prescribed.
• Most people who have primary thrombocythemia will live a normal lifespan. The outlook for secondary thrombocytosis depends on its underlying cause.