Your clotting cells (platelets) are produced in the bone marrow and help control bleeding. Sometimes too few platelets are produced or are destroyed too quickly, resulting in a condition known as thrombocytopenia. This can be caused by immune disorders, some medication, liver disease, or chronic bleeding. A high platelet count is called thrombocytosis and can be caused by several conditions, including bone marrow disorders, infection and inflammation. Read more about what blood is, the different blood types, and the main functions of blood in our blog: what is blood and what does it do?