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Polycythemia vera is a blood disorder in which your bone marrow makes too many red blood cells. Polycythemia vera also may result in production of too many of the other types of blood cells — white blood cells and platelets. But it's the excess red blood cells that thicken your blood and cause most of the concerns associated with polycythemia vera.

Polycythemia vera — also called primary polycythemia — is rare and usually develops slowly. You may have it for years without noticing signs or symptoms. Often, polycythemia vera is found during a blood test done for some other reason.

Without treatment, polycythemia vera can be life-threatening. However, with proper medical care, many people experience few problems related to this disease.

In its early stages, polycythemia vera usually doesn't cause any signs or symptoms. However, as the disease progresses, you may experience:

• Headache
• Dizziness
• Itchiness, especially following a warm bath or shower
• Redness of your skin
• Shortness of breath
• Breathing difficulty when you lie down
• Numbness, tingling, burning or weakness in your hands, feet, arms or legs
• Chest pain
• A feeling of fullness or bloating in your left upper abdomen due to an enlarged spleen
• Fatigue

When to see a doctor
Make an appointment with your doctor for an evaluation if you have any of the signs or symptoms of polycythemia vera.

Because polycythemia vera causes your blood to thicken and slows blood flow, it increases your risk of developing blood clots. If a blood clot occurs in your head, it can cause a stroke. Seek emergency medical care if you have any of the following signs or symptoms of a stroke:

• Sudden numbness, weakness, or paralysis of your face, arm or leg — usually on one side of your body
• Sudden difficulty speaking or understanding speech (aphasia)
• Sudden blurred, double or decreased vision
• Sudden dizziness, loss of balance or loss of coordination
• A sudden, severe headache or an unusual headache, which may be accompanied by a stiff neck, facial pain, pain between your eyes, vomiting or altered consciousness
• Confusion, or problems with memory, spatial orientation or perception

Blood consists of liquid, called plasma, and three types of cells that float within the plasma:

• White blood cells. These blood cells fight infection.
• Platelets. These blood cells help your blood clot after a cut.
• Red blood cells (erythrocytes). These blood cells carry oxygen from your lungs, through your bloodstream, to your brain and your body's other organs and tissues. Your body needs a supply of oxygenated blood to function. Oxygenated blood helps give your body its energy and your skin a healthy glow.

Normally, your body carefully regulates the number of blood cells you have and the ratio of one type to another. But in conditions called myeloproliferative disorders, such as polycythemia vera, the mechanism your body uses to control the production of blood cells becomes impaired, and your bone marrow makes too many or too few of some blood cells.

Mutation causes the disorder
The problem with blood cell production associated with polycythemia vera is caused by a change, or mutation, to DNA in a single cell in your bone marrow. In polycythemia vera, researchers have found this mutation to be a change in a protein switch that tells the cells to grow. Specifically, it's a mutation in the protein JAK2 (the JAK2 V617F mutation). More than 90 percent of people with polycythemia vera, and about half the people with other myeloproliferative disorders, have this mutation. Doctors and researchers don't yet understand the full role of this mutation and its implications for treating the disease.

Your DNA is a set of instructions for your cells, telling them how and when to grow and divide. The DNA mutation responsible for polycythemia vera makes blood cell production go awry. All the cells produced by that first mutant cell have the same problem, and they dominate your blood cell production.

The DNA mutation that causes polycythemia vera occurs after conception — meaning that your mother and father don't have it — so it's acquired, rather than inherited from a parent. Researchers and doctors don't know what causes the mutation.

Some factors may increase your risk of developing polycythemia vera:

• Age. According to the National Heart, Lung, and Blood Institute, polycythemia vera is more common in adults older than 60. It's rare in people younger than 20.
• Sex. Polycythemia vera affects men more often than women.
• Family history. In some cases, polycythemia vera appears to run in families, indicating that genetic factors other than JAK2 may contribute to the disease.

Possible complications of polycythemia vera include:

• Blood clots. Polycythemia vera causes your blood to be thicker than normal, which can slow the rate of blood flow through your veins and arteries. Increased blood thickness and decreased blood flow, as well as abnormalities in your platelets, increase your risk of blood clots. Blood clots can cause a stroke, a heart attack, or blockage of an artery in your lungs (pulmonary embolism) or in a vein deep within a muscle (deep vein thrombosis).
• Enlarged spleen (splenomegaly). Your spleen helps your body fight infection and filter unwanted material, such as old or damaged blood cells. The increased number of blood cells caused by polycythemia vera makes your spleen work harder than normal, which causes it to enlarge. If your spleen becomes too large, it sometimes may need to be removed.
• Skin problems. Polycythemia vera may cause your skin to itch, especially after a warm bath or shower, or after sleeping in a warm bed. You may experience a burning or tingling sensation in your skin, particularly on your arms, legs, hands or feet. Your skin may also appear red, especially on your face, palms and earlobes.
• Problems due to high levels of red blood cells. Too many red blood cells can lead to a number of other complications, including open sores on the inside lining of your stomach, upper small intestine or esophagus (peptic ulcers), inflammation in your joints (gout), and uric acid stones in your kidneys.
• Other blood disorders. In rare cases, polycythemia vera may lead to other blood diseases, including a progressive disorder in which bone marrow is replaced with scar tissue (myelofibrosis), a condition in which stem cells don't mature or function properly (myelodysplastic syndrome), or cancer of the blood and bone marrow (acute leukemia).

You're likely to start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to a doctor who specializes in blood conditions (hematologist).

For the best care, it's a good idea to come prepared for your appointment. Write down any symptoms you're experiencing, including any that may seem minor or unrelated to the reason you scheduled the appointment. Be as specific as possible. If you're experiencing dizziness or shortness or breath, for instance, write down any activity that seemed to prompt it. If you have numbness or tingling, pinpoint where you're feeling those sensations. Also write down any questions you have for your doctor.

What to expect from your doctor
Your doctor is likely to ask you a number of questions, as well. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first begin experiencing symptoms?
• How frequent are your symptoms? For instance, do you notice dizziness, chest pain or itchiness every day? Several times a week?
• How severe are your symptoms?
• What, if anything, appears to worsen your symptoms? For instance, are you more short of breath when you lie down? Does your itchiness increase after a warm bath or shower?
• What, if anything, appears to improve your symptoms?

Blood tests
Doctors most frequently use blood tests to diagnose polycythemia vera. In fact, in many cases, polycythemia vera is discovered through blood tests performed for other reasons. If you have polycythemia vera, blood tests may reveal:

• An increase in the number of red blood cells and, in some cases, an increase in platelets or white blood cells.
• Elevated hematocrit measurement, the percentage of red blood cells that make up total blood volume.
• Elevated levels of hemoglobin, the iron-rich protein in red blood cells that carries oxygen.
• Lower than normal levels of oxygen in your blood.
• Very low levels of erythropoietin (EPO), a hormone that stimulates bone marrow to produce new red blood cells; the excess red blood cells turn off the production of EPO by your kidneys.

Bone marrow aspiration or biopsy
If your doctor suspects you have polycythemia vera, he or she may recommend a bone marrow aspiration or biopsy to collect a sample of your bone marrow. A bone marrow biopsy involves taking a sample of solid bone marrow material. A bone marrow aspiration is usually done at the same time as a biopsy. During an aspiration, your doctor withdraws a sample of the liquid portion of your marrow. To help you visualize this, think of your bone marrow as a moist sponge. Aspiration takes the liquid from the sponge. The biopsy takes a piece of the sponge.

If an examination of your bone marrow shows that it's producing higher than normal numbers of blood cells, it may be a sign of polycythemia vera. If you have polycythemia vera, analysis of your bone marrow or blood also may show the DNA change (JAK2 V617F mutation) that's associated with the disease.

Polycythemia vera is a chronic condition that can't be cured. Treatment focuses on reducing your amount of blood cells. In many cases, treatment can prevent complications from polycythemia vera and decrease or eliminate the disease's signs and symptoms.

Treatment may include:

• Phlebotomy. This is usually the first treatment option for most people with polycythemia vera. Phlebotomy involves drawing a certain amount of blood from one of your veins. This reduces the number of blood cells and decreases your blood volume, making it easier for your blood to function properly. How often you need phlebotomy depends on the severity of your condition.
• Medication to decrease blood cells. Phlebotomy alone may not be enough to control the signs, symptoms and complications of polycythemia vera in some people. If this is the case for you, your doctor may prescribe medications, such as hydroxyurea or anagrelide, to suppress your bone marrow's ability to produce blood cells. Radioactive phosphorus (phosphorus 32 or p-32) also can be used to reduce the number of red blood cells. Interferon-alpha may be used to stimulate your immune system to fight the overproduction of red blood cells.
• Low-dose aspirin. Your doctor may recommend that you take a low dose of aspirin to reduce your risk of blood clots. Low-dose aspirin may also help reduce burning pain in your feet or hands.
• Therapy to reduce itching. If you have bothersome itching, your doctor may prescribe medication, such as antihistamines or H-2-receptor blockers, or recommend ultraviolet light treatment to relieve your discomfort.

If you have polycythemia vera, be sure to:

• Exercise. Moderate exercise, such as walking, can improve your blood flow, which decreases your risk of blood clots. Leg and ankle stretches and exercises also can improve your blood circulation.
• Avoid tobacco. Using tobacco can cause your blood vessels to narrow, increasing the risk of heart attack or stroke due to blood clots.
• Be good to your skin. To reduce itching, bathe in cool water and pat your skin dry. Avoid hot tubs, heated whirlpools, and hot showers or baths. Try not to scratch, as it can damage your skin and increase the risk of infection. Use lotion to keep your skin moisturized.
• Avoid extreme temperatures. Poor blood flow increases your risk of injury from hot and cold temperatures. In cold weather, always wear warm clothing, particularly on your hands and feet. In hot weather, protect yourself from the sun and drink plenty of liquids.
• Watch for sores. Poor circulation can make it difficult for sores to heal, particularly on your hands and feet. Inspect your feet regularly and tell your doctor about any sores.