Polycythemia vera: symptoms, diagnosis, treatment and life expectancy

Most people who search for polycythemia vera have a blood count with a high hemoglobin or hematocrit on it, and most high results have a common cause: dehydration, smoking, sleep apnea, testosterone therapy or living at altitude. Polycythemia vera is the rare cause, usually found around age 60 ¹. What sets it apart is where the signal to make red cells comes from. Two tests show it: an erythropoietin (EPO) level, the kidney hormone that tells the marrow to make red cells, and a JAK2 gene test, a blood test for the gene change found in almost everyone with polycythemia vera. A low EPO with a positive JAK2 points to polycythemia vera.

Polycythemia, polycythemia vera and high hemoglobin are three different things

Polycythemia (also called erythrocytosis) means the blood holds more red cells than usual, seen on a blood count as a high hemoglobin, hematocrit or red blood cell count. Polycythemia vera is one specific cause of polycythemia. The difference lies in where the signal to make red cells comes from. In secondary polycythemia, the kidneys sense low oxygen (or a drug or tumor mimics that signal) and release more EPO. In polycythemia vera, the marrow makes red cells with no outside signal at all, so the body turns its EPO down.

As our high red blood cell count page puts it, "Most high results come from dehydration, smoking, testosterone therapy, sleep apnea or living at altitude." The American Family Physician review lists the same secondary causes ⁶. Testosterone therapy is a common reason for a man's hematocrit to rise above 50%; the low testosterone page covers that side, and the male hormone panel guide shows what to check alongside it.

Symptoms of polycythemia vera

Many people with polycythemia vera have no symptoms and learn about it from a routine blood count ⁶. When symptoms come, they fall into three groups.

Itching after a warm shower is the most distinctive of these. It is common in polycythemia vera and unusual in the secondary causes, so mention it to a doctor if a blood count shows high hemoglobin.

What a blood count shows in polycythemia vera

A complete blood count (CBC) is where polycythemia vera shows up first. The CBC explained page covers each line; the table below shows what polycythemia vera tends to do to the lines that matter here. Reference ranges and units vary by lab, sex and altitude.

Low MCV and low ferritin are common in polycythemia vera. Building so many red cells drains iron, and phlebotomy removes more, so a person with polycythemia vera can look iron deficient while their hemoglobin is still high ¹. A high red cell count with small red cells (low MCV) is a pattern doctors look for. The iron studies guide explains ferritin and the other iron markers.

A single high hematocrit calls for a repeat test. Dehydration from a hot day, a hard workout or fasting before the draw can push hematocrit up a few points, which is why the trend beats a single reading.

How PV is diagnosed: JAK2, EPO and the bone marrow

Doctors use the World Health Organization (WHO) criteria, revised in 2016 ² and kept in the 2022 WHO and International Consensus Classification (ICC) updates ¹. Diagnosis needs all three major criteria, or the first two major criteria plus the minor one.

A bone marrow biopsy may be skipped when hemoglobin is above 18.5 g/dL in men or 16.5 g/dL in women (hematocrit above 55.5% or 49.5%) and the JAK2 test is positive with a low EPO ². The biopsy is still often done, because it shows early scarring (fibrosis) that changes the outlook ¹.

A low EPO is highly specific for polycythemia vera, but a normal EPO does not rule it out, which is why the JAK2 test carries more weight ¹. Doctors often add ferritin, lactate dehydrogenase (LDH) and uric acid, which rise or fall with marrow activity.

Is polycythemia vera cancer, and is it inherited?

Polycythemia vera is classed as a blood cancer, one of the myeloproliferative neoplasms. It is a chronic, slow cancer that most people live with for many years, and it is treated mainly to prevent clots.

Polycythemia vera is not inherited the way eye color is. The JAK2 mutation arises during life in a single marrow stem cell, and it is not in the egg or sperm cells passed to children. Close relatives of someone with polycythemia vera have a modestly higher risk of a myeloproliferative neoplasm, so a small inherited tendency exists, but most people with polycythemia vera have no affected relatives ¹.

Treatment keeps the blood thin enough to prevent clots

Every polycythemia vera treatment serves one goal, which is preventing clots. Roughly 1 in 5 people have already had a clot by the time they are diagnosed, and arterial clots (stroke, heart attack) are more common than venous ones ⁵.

Phlebotomy, the removal of blood much like a donation, lowers hematocrit quickly. The CYTO-PV trial randomized 365 people to a hematocrit target under 45% or a looser 45% to 50% target; cardiovascular death or a major clot happened in 2.7% of the stricter group and 9.8% of the looser group ³.

Low-dose aspirin is added for most people. In the ECLAP trial, 100 mg of aspirin a day cut the combined risk of heart attack, stroke, pulmonary embolism, major vein clots or cardiovascular death by about 60%, with no significant rise in major bleeding ⁴. Aspirin is a medical decision in polycythemia vera, because a very high platelet count can cause bleeding, so the choice belongs to the hematologist. The clotting tests guide covers the bleeding and clotting checks that may sit beside it.

Doctors then sort people into two risk groups, and the group decides whether a cell-lowering drug (cytoreduction) is added ¹.

Ropeginterferon alfa-2b was approved by the FDA in November 2021 for adults with polycythemia vera regardless of earlier treatment, and interferons are often preferred for younger people and during pregnancy ¹. Cell-lowering drugs are also used for low-risk people with troublesome symptoms, a growing spleen or a rising white count.

Life expectancy and what can change over time

In a study of 1,545 people with polycythemia vera from Mayo Clinic and international centers, median survival was about 14 years overall and about 24 years for people diagnosed before age 60 ⁵. Older age, a higher white count, a past vein clot (venous thrombosis) and an abnormal chromosome test were linked to shorter survival in that study. Many people, especially those diagnosed young, live for decades with the condition, although survival in that study was still shorter than in people of the same age without it ⁵.

Over many years, polycythemia vera can change. A minority develop post-PV myelofibrosis, where the marrow scars and the blood count may fall rather than rise; fewer develop acute myeloid leukemia. Ten-year risks are under about 10% for myelofibrosis and under about 3% for leukemia, and the leukemia risk is higher after some older drugs, such as pipobroman, chlorambucil and radioactive phosphorus ¹. A falling hemoglobin without phlebotomy, a growing spleen, weight loss or drenching sweats are reasons to see the hematologist sooner than planned.

Living with polycythemia vera

Blood counts are checked every few weeks at the start and every few months once hematocrit is stable. Drinking normally and keeping the same routine before each draw keeps results comparable; the guide on preparing for a blood test covers the details. Not smoking, keeping blood pressure and cholesterol in check, and staying active all lower clot risk, the main threat in polycythemia vera.

• Long flights and car trips raise clot risk: get up and walk, flex the calves and drink water.
• Lukewarm showers, patting dry and moisturizing help some people with aquagenic itch; treatment that controls the counts often eases it too.
• Pregnancy with polycythemia vera needs a hematologist and obstetrician planning together, because clot and miscarriage risks are higher and some drugs are unsafe in pregnancy.
• Surgery and dental work need the hematologist told in advance, because both clot and bleeding risks change.

What to do if your hemoglobin or hematocrit is high

1. 1Repeat itAsk the clinician who ordered the test about a repeat blood count after a normal day of drinking fluids. A one-off high hematocrit from dehydration often settles.
2. 2Look at the rest of the blood countHigh hemoglobin alone points more toward a secondary cause; high hemoglobin with a high platelet count or white count, or a large spleen, makes polycythemia vera more likely.
3. 3Check the common causesSmoking, snoring with daytime sleepiness (possible sleep apnea), testosterone therapy, SGLT2 inhibitor diabetes drugs and living at altitude all raise hemoglobin.
4. 4Ask about EPO and JAK2If hemoglobin or hematocrit stays above the threshold with no clear cause, an EPO level and a JAK2 test are the usual next tests, and a referral to a hematologist follows if JAK2 is positive. If JAK2 is negative and EPO is normal or high, polycythemia vera is unlikely; the next step is usually a search for a secondary cause, such as a sleep study for snoring or a review of medicines, with a recheck of the count.

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