PV disease, or polycythemia vera, is a blood cancer in which your bone marrow produces too many red blood cells. It belongs to a group of cancers called myeloproliferative neoplasms, meaning the bone marrow grows cells in an uncontrolled way. The excess red blood cells thicken your blood, raising the risk of dangerous blood clots. With proper management, most people with PV live for many years after diagnosis.
What Causes Polycythemia Vera
Nearly all cases of PV trace back to a single genetic mutation. About 95% of people with PV carry a mutation called JAK2 V617F. This mutation acts like a stuck “on” switch in the bone marrow, telling stem cells to keep producing red blood cells even when the body doesn’t need them. A small number of remaining cases involve a different mutation in the same gene.
The JAK2 mutation is almost always acquired during a person’s lifetime rather than inherited from a parent. Researchers still don’t fully understand what triggers it. Having the mutation doesn’t guarantee you’ll develop PV, but it’s present in virtually every confirmed case and is a cornerstone of diagnosis.
Common Symptoms
PV often develops slowly, and some people have no noticeable symptoms for years. When symptoms do appear, they stem from thickened blood and the overactive bone marrow. Common signs include:
- Itching after a warm bath or shower. This is one of the most distinctive symptoms of PV, sometimes called aquagenic pruritus. It can range from mild tingling to intense, widespread itching.
- Burning, tingling, or redness in the hands and feet. This painful sensation, known as erythromelalgia, results from impaired blood flow in small vessels.
- Headaches, dizziness, and vision changes. Thickened blood moves more sluggishly through the brain’s blood vessels.
- Fatigue and weakness. Despite having extra red blood cells, many people with PV feel persistently tired.
- An enlarged spleen. The spleen works overtime filtering excess blood cells, which can cause fullness or pain in the upper left abdomen.
How PV Is Diagnosed
Diagnosis starts with blood tests. The current diagnostic thresholds look at hemoglobin and hematocrit levels: above 16.5 g/dL hemoglobin (or 49% hematocrit) in men, and above 16 g/dL (or 48% hematocrit) in women. These levels alone aren’t enough for a diagnosis. They need to be paired with a positive JAK2 mutation test, and a bone marrow biopsy is often recommended to confirm the findings and rule out other conditions.
PV is sometimes caught incidentally during routine blood work before any symptoms develop. An unusually high red blood cell count on a standard complete blood count panel is often the first clue.
Blood Clots: The Biggest Risk
The most serious complication of PV is blood clotting. Thickened blood is more prone to forming clots in both arteries and veins, which can lead to strokes, heart attacks, deep vein thrombosis, or pulmonary embolism. In a large study of Medicare patients with PV, 28.4% experienced a thrombotic event during a median follow-up of about three years, with ischemic stroke being the most common (46% of those events).
Two factors put you at highest risk for clots: being over 60 years old and having had a previous clot. If either applies to you, you’re considered high-risk and will typically need more aggressive treatment beyond basic blood draws.
How PV Is Managed
The primary goal of treatment is keeping your hematocrit below 45%. A landmark clinical trial published in the New England Journal of Medicine found that patients who maintained a hematocrit below 45% had significantly lower rates of cardiovascular death and major blood clots compared to those kept between 45% and 50%. That 45% target is now the standard benchmark.
The simplest way to lower hematocrit is therapeutic phlebotomy, which is essentially a scheduled blood draw. A unit of blood is removed at regular intervals to reduce the concentration of red blood cells. For many lower-risk patients, phlebotomy combined with low-dose aspirin is enough to manage the disease.
High-risk patients, those over 60 or with a history of clots, typically need additional medication to slow down the bone marrow’s overproduction. The two first-line options are hydroxyurea (a daily pill that suppresses blood cell production) and a long-acting interferon injection. Both are effective at controlling blood counts. If a patient can’t tolerate either of those, a targeted therapy called ruxolitinib, which directly blocks the overactive JAK2 pathway, can be used instead. The choice between these medications is highly individualized based on age, side effect profile, and how well blood counts respond.
Long-Term Outlook and Disease Progression
PV is a chronic condition, not a curable one, but most people live with it for many years. The disease can potentially transform into more serious blood cancers over time, though the odds remain relatively low for most patients.
The risk of PV progressing to myelofibrosis, a condition where scar tissue replaces healthy bone marrow, runs about 5 to 6% at 10 years after diagnosis and 6 to 14% at 15 years. The median time to this transformation is 8.5 to 20 years. Progression to acute myeloid leukemia is less common: roughly 2.3% at 10 years and 5.5% at 15 years in large studies, though smaller studies have reported higher rates. These transformations are more likely in patients who are older at diagnosis, have very high white blood cell counts, or have been on certain treatments for extended periods.
Regular monitoring with blood tests is a permanent part of living with PV. Most patients have blood counts checked every few months to make sure hematocrit stays below target and to watch for any signs that the disease is changing. With consistent management, the majority of people with PV maintain a good quality of life for decades after diagnosis.