PV is a disorder of the bone marrow that causes an overproduction of red blood cells, although white blood cell and platelet counts are also increased. The extra red blood cells make your blood thicker than it should be.
PV can occur at any age, but people over 50 are more likely to be affected. Men are slightly more likely to be diagnosed.
If you have PV, your blood sample will show you have too many red blood cells. You’ll also have other blood tests to measure substances including uric acid and oxygen, and you might have a test to check your blood is clotting normally. Chest X-rays, abdominal ultrasounds and CT scans may be used to rule out other diseases and to measure the size of your spleen and liver, which can become enlarged in PV. Finally, your doctor will use cytogenetic testing (testing of chromosomes in blood cells) to check for the JAK2V617F mutation, found in 90-95% of people with PV.
A lot of people don’t have symptoms to begin with and PV is often picked up during routine blood tests. When symptoms do occur, they usually develop gradually over time. Thicker blood increases your risk of blood clots forming and blocking veins or arteries, potentially causing a stroke or heart attack. Blood clots are a common complication of PV, affecting about 30% of people with the condition. As thicker blood flows around your body more slowly than it should, it may not get enough oxygen to your organs, which can cause other serious problems such as angina and heart failure (where your heart can’t pump enough blood around your body, leading to symptoms such as fatigue). And because your spleen tries to compensate by producing red blood cells, up to 75% of people with PV develop an enlarged spleen and some people also get an enlarged liver. As a result of what’s happening in your body, you might notice symptoms including:
One study asked 405 patients with PV about their most significant symptoms, the results showed that 85% had fatigue as a symptom, followed by itching reported by 65%. Other symptoms were night sweats (49%), bone pain (43%), fever (13%) weight loss (10%) and spleen pain (4%).
The cause of PV is unknown. However, it is known that the disease is driven by dysregulation of the JAK/STAT pathway that is involved in the blood cell production process in the bone marrow. Nearly all people with PV have a change (mutation) in a protein known as JAK2 (short for Janus kinase) that regulates blood cell production.
People are not born with these mutations but acquire them during their lives. It is also important to note that PV is not inherited and is not passed on from parent to child, although some families do seem to develop the disease more readily than others.
Your doctor might adopt a ‘watch and wait’ policy, simply monitoring you without further action, particularly in the early stages after your diagnosis. Further information about managing symptoms is available, Click here.
In about 15% of cases, PV can evolve into myelofibrosis (MF, known as post-polycythemia vera myelofibrosis or post-PV MF) and in a smaller number, it can progress to acute myeloid leukemia, which are both more serious conditions. But most people with PV live without complications for a long time, and it’s likely having it won’t have any effect on your life expectancy as long as your symptoms are monitored and managed.