What Causes Polycythemia Vera?

Polycythemia vera (PV) also is known as primary polycythemia. A mutation, or change, in the body's JAK2 gene is the main cause of PV. The JAK2 gene makes an important protein that helps the body produce blood cells.

What causes the change in the JAK2 gene isn't known. PV generally isn't passed from parent to child. However, in some families, the JAK2 gene may have a tendency to mutate. Other, unknown genetic factors also may play a role in causing PV.

Secondary Polycythemia

Another type of polycythemia, called secondary polycythemia, isn't related to the JAK2 gene. Long-term exposure to low oxygen levels causes secondary polycythemia.

A lack of oxygen over a long period can cause your body to make more of the hormone erythropoietin (EPO). High levels of EPO can prompt your body to make more red blood cells than normal. This leads to thicker blood, as seen in PV.

People who smoke, spend long hours at high altitudes, or have severe lung or heart disease may develop secondary polycythemia.

Rarely, tumors can make and release EPO, or certain blood problems can cause the body to make more EPO.

Sometimes secondary polycythemia can be cured-it depends on whether the underlying cause can be stopped, controlled, or cured.