What is Polycythaemia Vera?
Polycythaemia vera, often shortened to PV, is a chronic blood disorder that affects how your bone marrow produces blood cells. The bone marrow is the soft, spongy tissue inside your bones where new blood cells are made. In healthy people, the bone marrow creates a balanced number of red blood cells, white blood cells, and platelets. However, in people with polycythaemia vera, the bone marrow produces too many red blood cells, and often too many white blood cells and platelets as well.[1]
This overproduction causes the blood to become thick and sticky, which slows down how it flows through your blood vessels. When blood moves more slowly, it doesn’t carry oxygen efficiently to your body’s tissues and organs. The thicker blood also increases the likelihood of blood clots, which are solid lumps that form when blood cells stick together. These clots can block blood vessels and lead to life-threatening problems such as heart attacks, strokes, or blockages in the lungs.[2]
Polycythaemia vera is classified as a myeloproliferative neoplasm, which is a type of blood cancer. The term “myeloproliferative” refers to the bone marrow producing too many cells, and “neoplasm” means an abnormal growth of tissue. However, this cancer is different from many others because it develops very slowly over many years. Most people with PV can manage their symptoms and live for a long time with appropriate treatment.[2]
The condition is also known by several other names, including primary polycythaemia, polycythaemia rubra vera, and Osler-Vaquez disease. All of these terms refer to the same disorder.[2]
How Common is Polycythaemia Vera?
Polycythaemia vera is a rare disease. It affects roughly 50 out of every 100,000 people in the United States, though estimates vary slightly depending on the study. In some reports, the rate ranges from 0.6 to 1.6 cases per million people.[2][3]
The disease can affect people of all ethnic backgrounds and both men and women. However, men are slightly more likely than women to develop the condition. While PV can occur at any age, it is most commonly diagnosed in older adults. The median age at diagnosis is around 60 years, meaning that half of all people diagnosed are younger than 60 and half are older. It is rare for anyone under the age of 40 to receive this diagnosis.[3][6]
Studies have also shown that there are fewer cases of polycythaemia vera in Japan compared to the United States or Europe, suggesting that there may be some geographical or ethnic differences in how often the disease occurs.[3]
What Causes Polycythaemia Vera?
The root cause of polycythaemia vera is a genetic mutation, which is a change in the instructions inside your cells that tell them how to grow and function. This mutation is not something people are born with in most cases. Instead, it develops at some point during a person’s life for reasons that are not yet fully understood.[2]
Nearly all people with PV—about 95 to 98 percent—have a mutation in a gene called JAK2. The most common version of this mutation is known as JAK2V617F. This mutation causes certain proteins inside blood-forming cells to become overactive, particularly those involved in responding to signals that tell the body to make more red blood cells. Because of this, the bone marrow produces far too many red blood cells, even when the body doesn’t need them.[3][5][7]
In a smaller number of patients, other mutations in the JAK2 gene, such as those affecting exon 12, have also been identified. Regardless of the exact mutation, the result is the same: the bone marrow receives faulty signals and produces too many blood cells.[7]
Importantly, this mutation is not inherited from parents in the vast majority of cases. It happens randomly during a person’s lifetime. However, in very rare situations, there may be families where more than one member develops the disease, suggesting that in some cases genetic factors might play a role.[6]
Some studies have also suggested that exposure to intense radiation or toxic substances might increase the risk of developing PV, but these links are not fully proven.[5]
Who is at Risk for Polycythaemia Vera?
While polycythaemia vera can happen to anyone, certain groups of people are more likely to develop the disease. Age is one of the strongest risk factors. People over the age of 60 are most commonly diagnosed, although younger individuals can also be affected. The disease is rare in people under 40.[2][3]
Men have a slightly higher chance of developing PV compared to women, though the difference is not very large.[3]
Having the JAK2 mutation significantly increases the risk of developing polycythaemia vera. Around 95 percent of people with PV test positive for this mutation. In the general population, only about 0.1 to 0.2 percent of people carry this mutation without having the disease.[7]
As mentioned earlier, exposure to high levels of radiation may increase risk, and there are also suggestions that certain environmental toxins might contribute, though these are not firmly established causes.[5]
What are the Symptoms of Polycythaemia Vera?
Many people with polycythaemia vera do not notice any symptoms at first. In fact, the condition is often discovered accidentally during a routine blood test that shows unusually high levels of red blood cells. As the disease progresses, however, various symptoms may appear. These symptoms are caused by the thickened blood, reduced oxygen delivery to tissues, and the body’s struggle to cope with too many blood cells.[1][6]
One of the most characteristic symptoms is intense itching, especially after taking a warm bath or shower. This happens because extra red blood cells trigger the release of a chemical called histamine, which can irritate the skin. Between 40 and 55 percent of people with PV experience this kind of itching.[7]
Another common symptom is a reddish or purple discoloration of the skin, particularly on the face. This happens because there are so many red blood cells in the blood vessels near the skin’s surface. People sometimes describe this as looking like a sunburn or a persistent blush.[1][6]
Headaches, dizziness, and problems with vision—such as blurred vision, double vision, or temporary blind spots—are also reported. These occur because the thick blood does not flow smoothly through the small blood vessels in the brain and eyes.[1][5]
Some people feel a burning or tingling sensation in their hands and feet, often accompanied by redness and swelling. This is called erythromelalgia, and it results from tiny blood clots forming in the blood vessels of the extremities. It typically responds well to treatment with aspirin.[7]
Fatigue is another frequent complaint. People with PV often feel unusually tired, even after getting enough rest. This tiredness is partly due to the body working harder to pump thick blood through the circulatory system, and partly because the organs and tissues are not getting enough oxygen.[5]
A feeling of fullness or discomfort in the upper left side of the abdomen can occur if the spleen becomes enlarged. The spleen is an organ that filters blood and removes old or damaged blood cells. In PV, it has to work overtime to filter the extra cells, which can cause it to swell. This swelling is called splenomegaly.[1][2]
Other symptoms include night sweats, unexpected weight loss, shortness of breath (especially when lying down), and painful swelling in one joint, often the big toe. The joint pain is usually due to a condition called gout, which happens when uric acid builds up in the joints. High uric acid levels result from the rapid breakdown of extra blood cells.[1][2]
Some people also experience unusual bleeding, such as nosebleeds or bleeding gums, even though their blood has too many cells. This happens because the blood cells do not always function normally.[1]
How Does Polycythaemia Vera Affect the Body?
Polycythaemia vera changes how your blood and circulatory system work. Normally, red blood cells carry oxygen from your lungs to every part of your body. They are flexible and move easily through even the smallest blood vessels. But when there are too many red blood cells, the blood becomes thicker, almost like syrup instead of water. This makes it harder for the heart to pump blood, and the blood moves more slowly through the vessels.[2]
Because the blood is thick and sluggish, it cannot deliver oxygen efficiently. Organs and tissues that need oxygen may start to suffer. This is why people with PV often feel tired and may have trouble concentrating. It also explains why they can develop headaches and vision problems—because the brain and eyes are not getting enough oxygen.[2]
The slow-moving, thick blood is also more likely to form clots. Blood clots can stick to the walls of blood vessels or break free and travel through the bloodstream. If a clot blocks a blood vessel leading to the brain, it can cause a stroke. If it blocks a vessel in the heart, it can cause a heart attack. A clot that lodges in the lungs is called a pulmonary embolism, and it can lead to serious breathing problems and heart failure.[2]
The extra red blood cells also put stress on the spleen, the organ responsible for filtering old blood cells. As the spleen works harder, it can become swollen and tender. Over time, this can cause pain and a feeling of fullness in the left side of the abdomen.[2]
The rapid turnover of so many blood cells produces high levels of uric acid, a waste product. When uric acid builds up, it can form crystals in the joints, causing painful swelling known as gout. It can also accumulate in the kidneys, leading to kidney stones.[2]
In addition, the extra red blood cells trigger the immune system to release histamine, a chemical involved in fighting infections. In response, the stomach produces more acid, which can lead to stomach ulcers.[2]
What are the Complications of Polycythaemia Vera?
The most serious and immediate risk from polycythaemia vera is the formation of blood clots, also called thrombosis. Blood clots can form in arteries or veins and can travel to critical organs. A clot that reaches the brain can cause a stroke, while one that blocks a coronary artery in the heart can cause a heart attack. Clots in the lungs can lead to pulmonary embolism, a condition that makes it hard to breathe and can damage the heart. Blood clots in the veins, known as venous thromboembolism, can cause tissue damage and chronic problems with circulation.[2][6]
A particularly dangerous type of clot can block the main vein leading to the liver, a condition called Budd-Chiari syndrome. This causes blood to back up into the liver, leading to swelling, yellowing of the skin (jaundice), and liver failure.[2]
Over time, polycythaemia vera can lead to several secondary health problems. As mentioned, high uric acid levels can cause gout and kidney stones. Increased stomach acid can result in painful ulcers in the stomach lining.[2]
In rare cases, polycythaemia vera can progress to more aggressive forms of blood cancer. About 15 percent of patients may develop myelofibrosis, a condition where the bone marrow becomes filled with scar tissue and can no longer produce blood cells properly. An even smaller number of patients may develop acute myeloid leukemia, a fast-growing cancer of the blood and bone marrow.[4][5]
How is Polycythaemia Vera Diagnosed?
Diagnosing polycythaemia vera usually begins with a routine blood test that shows higher-than-normal levels of red blood cells. If your doctor sees these results, they will perform additional tests to confirm the diagnosis and rule out other conditions.[1][4]
A complete blood count, or CBC, is one of the first tests. This measures the number of red blood cells, white blood cells, and platelets in your blood. It also measures the hematocrit, which is the percentage of your blood that is made up of red blood cells, and the hemoglobin level, which is the amount of oxygen-carrying protein in your red blood cells. In PV, both the hematocrit and hemoglobin levels are usually higher than normal.[4][9]
Your doctor may also check the level of a hormone called erythropoietin, or EPO. This hormone is produced by the kidneys and tells the bone marrow to make more red blood cells. In people with polycythaemia vera, the EPO level is usually low because the body is already making too many red blood cells and doesn’t need more.[4][7]
A very important test is the genetic test for the JAK2 mutation. About 95 percent of people with PV test positive for the JAK2V617F mutation. If this mutation is found, it strongly supports the diagnosis of polycythaemia vera.[5][9]
Your doctor may recommend a bone marrow biopsy or bone marrow aspiration. In this procedure, a small sample of bone marrow is taken, usually from the hip bone, and examined under a microscope. The bone marrow in people with PV typically shows an excess of precursor cells that develop into red blood cells, and sometimes an increase in white blood cells and platelets as well.[4][9]
Other blood tests may include checking uric acid levels, vitamin B12 levels, and liver and kidney function. These help your doctor understand the overall impact of the disease on your body.[4]
How is Polycythaemia Vera Treated?
There is currently no cure for polycythaemia vera, but treatment can help control symptoms, reduce the risk of complications, and improve quality of life. The main goals of treatment are to lower the number of red blood cells in the blood, prevent blood clots, and manage any symptoms that arise.[1][9]
The most common treatment is a procedure called phlebotomy, which is similar to donating blood. A healthcare professional inserts a needle into a vein and withdraws a unit of blood, usually about one pint or half a liter. This reduces the volume of blood and the number of red blood cells. How often you need phlebotomy depends on how high your red blood cell count is. Some people may need the procedure every few weeks, while others may need it less often. The goal is to keep the hematocrit below 45 percent.[4][9]
Many people with polycythaemia vera take a low dose of aspirin every day. Aspirin helps prevent blood clots by making platelets less sticky. This can reduce the risk of heart attacks, strokes, and other clot-related complications. It can also help with symptoms like burning sensations in the hands and feet.[4][9]
For people who need additional help controlling their blood cell counts, doctors may prescribe medications. One common drug is hydroxyurea, a type of chemotherapy in pill form. It works by slowing down the bone marrow’s production of blood cells. Hydroxyurea is often used when the numbers of white blood cells and platelets are also high.[4][9]
Another medication is ruxolitinib, which is a drug that targets the JAK2 mutation. It can reduce the number of red blood cells, shrink an enlarged spleen, and relieve symptoms. Ruxolitinib is usually prescribed when hydroxyurea has not worked well or when a person cannot tolerate it.[4][9]
Interferons are another treatment option. These are proteins that help regulate the immune system and can lower blood cell counts. Interferons are sometimes used in younger patients or in pregnant women because they are safer in certain situations.[4][9]
If itching is a major problem, treatments may include antihistamines, light therapy, or certain types of antidepressants such as selective serotonin reuptake inhibitors (SSRIs), which have been found to help reduce itching in some patients.[4]
Managing symptoms like gout involves medications such as allopurinol, which lowers uric acid levels in the body and prevents painful flare-ups.[4]
Regular monitoring is essential. Your doctor will check your blood counts frequently to make sure your treatment is working and to adjust it as needed.[9]
Can Polycythaemia Vera be Prevented?
Because polycythaemia vera is caused by a genetic mutation that occurs randomly during a person’s life, there is no known way to prevent the disease from developing in the first place. The mutation is not inherited in most cases, and it is not caused by lifestyle choices or behaviors.[2]
However, once someone has been diagnosed with PV, there are steps they can take to help prevent complications and manage the disease more effectively. Staying hydrated is important because drinking plenty of fluids helps thin the blood and improve circulation. The general recommendation is to drink six to eight glasses of water or other low-fat, low-sugar drinks every day.[15]
If you smoke, quitting is one of the most important things you can do. Smoking increases the risk of blood clots, and because PV already increases this risk, the combination can be especially dangerous. Many resources and support services are available to help people stop smoking.[15]
Staying physically active is also beneficial. Regular exercise improves blood flow, reduces the risk of clots, and helps combat fatigue. Even light exercise, such as walking, can make a difference. It’s important to start slowly and gradually build up your activity level.[15]
Eating a healthy, balanced diet can help you maintain a healthy weight and support overall well-being. Some people with PV may need to avoid foods high in iron, as iron can contribute to higher red blood cell production. Your doctor or a dietitian can provide guidance tailored to your situation.[15]
It’s also important to attend all scheduled medical appointments and follow your doctor’s recommendations. Regular monitoring of your blood counts and symptoms allows for timely adjustments to your treatment plan, which can prevent serious complications.[9]
