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 a protein that helps the body produce blood cells.
What causes the change in the JAK2 gene isn't known. PV generally isn't inherited—that is, passed from parents to children through genes. 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.
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 have severe heart or lung disease may develop secondary polycythemia. People who smoke, spend long hours at high altitudes, or are exposed to high levels of carbon monoxide where they work or live also are at risk.
For example, working in an underground parking garage or living in a home with a poorly vented fireplace or furnace can raise your risk for secondary polycythemia.
Rarely, tumors can make and release EPO, or certain blood problems can cause the body to make more EPO.
Sometimes doctors can cure secondary polycythemia—it depends on whether the underlying cause can be stopped, controlled, or cured.