Polycythemia vera (PV) is treated by keeping your red blood cell count low enough to prevent dangerous blood clots. The central target is a hematocrit level below 45%, a threshold established by the landmark CYTO-PV trial, which found that patients maintained above 45% were nearly four times more likely to die from cardiovascular causes or suffer a major clot. Treatment combines blood removal, daily low-dose aspirin, and, for higher-risk patients, medications that slow red blood cell production.
Why the 45% Hematocrit Target Matters
Hematocrit measures the percentage of your blood that’s made up of red blood cells. In PV, your bone marrow overproduces these cells, thickening your blood and raising the risk of stroke, heart attack, and clots in veins. The CYTO-PV trial randomized patients to either a strict target (below 45%) or a looser one (45 to 50%). After a median follow-up of about two and a half years, only 2.7% of patients in the strict group experienced a major cardiovascular event, compared with 9.8% in the looser group. That difference is why virtually every current guideline centers on keeping hematocrit below 45%.
Phlebotomy: The First-Line Treatment
Phlebotomy is simply a controlled blood draw, similar to donating blood. By removing a unit of blood at regular intervals, your body’s red blood cell volume drops and your hematocrit falls toward the target. Most people start with sessions every one to two weeks until their hematocrit is under 45%, then shift to a maintenance schedule that varies from person to person. Some need blood drawn every month or two; others go longer between sessions.
The procedure takes about 15 to 30 minutes and is done in a clinic or infusion center. You may feel lightheaded or tired afterward, especially during the early intensive phase. Staying well-hydrated before and after each session helps. Over time, frequent phlebotomy depletes your iron stores, which actually helps slow red blood cell production. Your doctor will monitor your iron levels but typically won’t supplement iron unless you develop significant symptoms from deficiency, since doing so would counteract the treatment.
Low-Dose Aspirin
Nearly everyone with PV takes a daily low-dose aspirin. It works by making platelets less sticky, which reduces the chance of clots forming in arteries and veins. Aspirin also helps with one of PV’s most common vascular symptoms: burning, redness, and pain in the hands and feet (called erythromelalgia). There’s also evidence it can ease the intense itching some patients experience after contact with water.
Aspirin is straightforward and well-tolerated for most people. The main risk is bleeding, particularly in the stomach, so your doctor will weigh that against your clot risk before prescribing it.
How Risk Level Shapes Your Treatment
PV treatment is divided into two broad categories based on your risk of blood clots. The two factors that matter most are age and clotting history. Patients under 60 with no prior blood clots are considered low risk. Patients 60 or older, or anyone who has already had a clot, are classified as high risk.
If you’re low risk, phlebotomy plus aspirin may be all you need. The goal is to keep your hematocrit below 45% with the fewest interventions possible. If you’re high risk, you’ll also start a cytoreductive medication, a drug that tells your bone marrow to slow down its overproduction of blood cells. This extra layer of protection significantly lowers the chance of a life-threatening clot.
Cytoreductive Medications
Hydroxyurea
Hydroxyurea has been the most widely used cytoreductive drug for PV for decades. It’s an oral medication, typically started at 500 mg twice daily, that suppresses the bone marrow’s overactivity. Most patients see their blood counts drop within weeks, and phlebotomy becomes less frequent or unnecessary. Blood counts need regular monitoring, usually every few weeks at first and then every few months once stable, because the dose often needs adjusting.
Hydroxyurea works well for most people, but some develop resistance or intolerance over time. Resistance usually means your hematocrit stays at or above 45% despite adequate dosing, or your PV-related symptoms persist. Intolerance typically shows up as nausea, vomiting, or mouth sores. In one real-world study, about 78% of patients who stopped hydroxyurea did so because of resistance, and 28% because of intolerance, with some experiencing both.
Ropeginterferon Alfa-2b
A newer option, ropeginterferon alfa-2b, has gained significant ground. The NCCN now lists it as a preferred treatment for both low-risk and high-risk PV, regardless of whether you’ve had prior treatment. Unlike hydroxyurea, which only controls blood counts, this interferon-based therapy can reduce the burden of the abnormal cells driving the disease.
Long-term data from the PROUD-PV and CONTINUATION-PV trials are notable. After 7.5 years of treatment, 61% of patients had a complete blood count response, and 80% had at least a partial one. By the sixth year, over 81% of patients on the drug needed no phlebotomies at all, compared with 60% on other standard treatments. Patients also reported lower symptom burden over time, with improvements in fatigue, itching, abdominal discomfort, and other common PV complaints. The drug is given as an injection, typically every two weeks, which some patients prefer over daily pills.
Ruxolitinib
If hydroxyurea stops working or you can’t tolerate it, ruxolitinib is the established second-line option. It works by blocking the overactive signaling pathway (driven by the JAK2 mutation present in nearly all PV patients) that causes the bone marrow to overproduce cells. Ruxolitinib is particularly effective at controlling an enlarged spleen and reducing the symptom burden that can persist despite other treatments, including fatigue, night sweats, and itching.
Managing Itching and Other Symptoms
One of PV’s most frustrating symptoms is aquagenic pruritus, an intense itching triggered by contact with water. It can make showers miserable and significantly affect quality of life. Standard antihistamines are largely ineffective for this type of itch. Aspirin helps some people, likely because platelets and inflammatory compounds called prostaglandins play a role.
Other approaches that have shown benefit include adding sodium bicarbonate (baking soda) to bathwater to alkalize it, narrowband UVB light therapy, and certain antidepressants in the SSRI class like paroxetine. Pregabalin, a nerve pain medication, and naltrexone have also produced favorable results. For patients whose itching is driven heavily by their JAK2 mutation, ruxolitinib can be particularly effective. The good news is that as your hematocrit comes under control and cytoreductive therapy takes effect, itching often improves as well.
Fatigue is another hallmark symptom. It doesn’t always correlate with blood counts, meaning you can still feel exhausted even when your numbers look good. Ropeginterferon alfa-2b has shown the most consistent long-term improvement in fatigue scores among the available medications.
Long-Term Outlook and Disease Progression
PV is a chronic condition, but most people live with it for many years with proper treatment. The main long-term concerns, beyond clotting, are the small but real chances of the disease transforming into a more serious blood disorder. At the 10-year mark, roughly 12% of PV patients develop myelofibrosis, a condition where scar tissue builds up in the bone marrow. By 15 years, that figure rises to about 25%. The risk of transformation to acute leukemia is lower: around 3% at 10 years and roughly 8% at 15 years.
These numbers underscore why ongoing monitoring matters even when you feel well. Regular blood work, periodic bone marrow evaluations, and symptom tracking help catch any shift in the disease early, when there are more options for managing it. Treatment choices made now, particularly keeping hematocrit tightly controlled and using cytoreductive therapy when indicated, are the best tools for reducing both clotting risk and the chance of progression.