The bone marrow produces platelets, also known as thrombocytes, and releases them into the circulation. These small blood elements are pieces of larger cells called megakaryocytes. Platelets interact with a group of blood proteins, the clotting factors, to form blood clots. The medical terms thrombocythemia and thrombocytosis refer to abnormally elevated platelet counts. Disorders of the bone marrow and systemic conditions can cause an elevated platelet count.
Essential Thrombocythemia
Essential thrombocythemia is an abnormality of the bone marrow megakaryocytes, which causes an overproduction of platelets. The National Heart, Lung and Blood Institute notes that the platelets produced in essential thrombocythemia are abnormal. They may cause spontaneous formation of blood clots due to increased stickiness. Alternatively, they may not interact normally with the clotting factors; this leads to easy bruising and bleeding. The National Cancer Institute advises that people with essential thrombocythemia have an increased risk of developing acute leukemia.
Polycythemia Vera
Polycythemia vera is an uncommon condition in which the bone marrow produces too many red blood cells. Platelet production is typically also markedly increased. The increased number of red blood cells makes the blood abnormally thick, which slows normal flow. According to the Mayo Clinic, possible symptoms of polycythemia vera include a ruddy skin complexion, headaches, shortness of breath, dizziness, chest pain and fatigue. The mainstay of treatment for polycythemia vera is periodic therapeutic phlebotomy--drawing blood from the circulation to reduce the number of circulating blood cells. People with polycythemia vera have an increased risk for acute leukemia.
Cancer
An abnormally high platelet count caused by another condition is called secondary or reactive thrombocytosis. Cancer is a common cause of secondary thrombocytosis. According to the National Heart, Lung and Blood Institute, up to 35 percent of people with cancer have an elevated platelet count. Cancers of the colon, stomach, lung, breast and ovary and lymphoma are associated with increased platelet counts. Notably, the presence of an elevated platelet count is often an indicator of poor long-term prognosis among people with cancer. In a 2008 research article published in "Interactive Cardiovascular and Thoracic Surgery," Dr. M. Tomita and colleagues reported the five-year survival among people operated on for lung cancer who had elevated platelet counts was less than one-half that of people undergoing the same surgery with normal platelet counts.
Iron-Deficiency and Hemolytic Anemia
People with iron-deficiency or hemolytic anemia may have secondary thrombocytosis, reports the Mayo Clinic. Although the association between these forms of anemia and secondary thrombocytosis is well established, the precise mechanism by which this phenomenon occurs remains an area of active medical research.
References
- National Heart, Lung and Blood Institute: What Causes Thrombocythemia and Thrombocytosis?
- Merck Manual for Healthcare Professionals: Essential Thrombocythemia
- National Cancer Institute: Essential Thrombocythemia
- American Family Physician: Polycythemia Vera
- National Heart, Lung and Blood Institute: Polycythemia Vera, Signs and Symptoms
