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Polycythemia vera, or PV, is a rare blood disease in which the body makes too many red blood cells. These extra red blood cells make blood thicker than normal. The thickened blood flows more slowly through small blood vessels and can form clots. These clots can cause heart attack and stroke. Thicker blood also flows more slowly to all parts of your body, preventing your organs from getting enough oxygen. This can cause other serious complications, such as angina and heart failure.
Polycythemia vera 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.
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.
Polycythemia vera (PV) develops slowly. The disease may not cause signs or symptoms for years.
When signs and symptoms do occur, they're the result of the thick blood that occurs with PV. This thickness slows the flow of oxygen-rich blood to all parts of your body. Without enough oxygen, many parts of your body won't work normally.
The most common signs and symptoms of PV include:
In rare cases, people who have PV may have pain in their bones.
There are a number of different blood tests to diagnose PV. These tests include a complete blood count (CBC) and other tests, if necessary.
Complete Blood Count
Often, the first test used to diagnose PV is a CBC. The CBC measures many different parts of your blood.
This test checks your hemoglobin and hematocrit levels. Hemoglobin is the iron-rich protein in red blood cells that carries oxygen to the body. Hematocrit is a measure of how much space red blood cells take up in your blood. A high level of hemoglobin or hematocrit may be a sign of PV.
The CBC also checks the number of red blood cells, white blood cells, and platelets in your blood. Abnormal results may be a sign of PV, a blood disorder, an infection, or another condition.
Other Blood Tests
Blood smear. For this test, a small sample of blood is drawn from a vein, usually in your arm. The sample of blood is put on a glass slide. A microscope is then used to look at your red blood cells.
A blood smear can show whether you have a higher-than-normal number of red blood cells. The test also can show abnormal types of blood cells that are linked to myelofibrosis and other conditions related to PV.
Erythropoietin level. This blood test measures the level of EPO in your blood. EPO is a hormone that stimulates bone marrow to make new blood cells. People who have PV have very low levels of EPO. People who have secondary polycythemia usually have normal or high levels of EPO.
Bone Marrow Tests
Bone marrow tests are used to check whether your bone marrow is healthy. These tests also show whether your bone marrow is making normal amounts of blood cells.
If the tests show that your bone marrow is making too many blood cells, it may be a sign that you have PV.