The word polycythemia simply means "many cells in the blood." There are two forms of this disease: polycythemia vera and secondary polycythemia.
Polycythemia vera (also called primary polycythemia) is a rare growth disorder of the bone marrow, occurring when the marrow is overactive and produces more blood cells than the body needs.
Secondary polycythemia affects some people as a result of limited oxygen due to smoking or living at high altitudes.
Polycythemia vera usually produces a high concentration of red blood cells or hemoglobin in the circulating blood, but it's important to note that white blood cell and platelet counts may also be increased.
Polycythemia vera stems from problems with the bone marrow. Bone marrow is found in the center of most bones and normally produces all red blood cells and platelets and most white blood cells. When this process breaks down, production of cells is no longer orderly and conditions such as polycythemia can result. Although the exact cause of polycythemia vera is unknown, researchers have found that a specific gene mutation is associated with almost all people with this condition.
Polycythemia vera is a rare condition usually affecting men in their 60s. It is more common in men than in women. The condition is rarely seen in people under age 40, but can also affect babies.
Although the cause of polycythemia vera is unknown, a number of factors are involved that appear to lead to secondary polycythemia. A high content of red blood cells builds up in response to low oxygen concentration in the air. Because there's less oxygen in the blood, the body attempts to overcome the lack by making more red blood cells. It doesn't stop, however, and keeps producing them until there are too many. The bone marrow can also be overstimulated by testosterone replacement therapy.
Living for long periods at high altitudes where there's less oxygen may lead to polycythemia. It also may occur in people with chronic lung conditions and certain kidney tumors and cysts. Heavy smoking is associated with an increase in carbon monoxide in the blood and may also lead to higher red cell and hemoglobin levels. Low blood oxygen levels (hypoxia) due to congenital heart disease also appear to be a factor in the development of polycythemia.
Most people who live at high altitudes don't appear to suffer secondary polycythemia. In fact, the condition is virtually absent in some mountain regions. When it does occur, it's thought that other environmental factors, such as smoking or mining, may contribute.
Polycythemia in babies usually occurs because the baby receives more than the normal amount of blood from the placenta during birth. It also can result from the mother living at a high altitude, or if the baby had a placenta that was not functioning optimally.