Essential thrombocythemia (ET) is a rare condition in which a person’s bone marrow makes too many blood platelets (also known as thrombocytes).
About half of people with ET have a mutation—or change—in a certain gene in the body.
Platelets travel through the body’s blood vessels. When a person damages a blood vessel—through a cut, for instance—platelets stick together to form clots and stop the bleeding. In people with ET, the bone marrow makes too many platelets, making it hard for the blood to flow. Unnecessary clots may form, and/or bleeding may increase.
Clotting can lead to serious health problems, like heart attack or stroke.
Learn what causes ET.