Testing for polycythemia vera (PV) typically starts with a standard blood draw and, depending on results, may involve genetic testing, a hormone level check, and a bone marrow biopsy. The current diagnostic guidelines require meeting a specific combination of criteria before a diagnosis is confirmed, so most people go through several tests rather than just one.
The First Step: A Complete Blood Count
A routine blood test is almost always where PV testing begins. The key numbers your doctor looks at are hemoglobin and hematocrit, which measure how much oxygen-carrying protein and how many red blood cells are packed into your blood. Under the 2022 WHO guidelines, the diagnostic thresholds are a hemoglobin above 16.5 g/dL in men or above 16 g/dL in women, or a hematocrit above 49% in men or above 48% in women.
These cutoffs are lower than many people expect. An elevated hemoglobin alone doesn’t confirm PV, since dehydration, smoking, sleep apnea, and living at high altitude can all push red blood cell counts up. But crossing these thresholds is what triggers the next round of testing.
JAK2 Genetic Testing
The single most important test in a PV workup is a blood test for mutations in the JAK2 gene. This gene controls a signaling pathway that tells your bone marrow how many blood cells to make. When it’s mutated, the marrow overproduces cells without the normal “stop” signals. About 95% of people with PV carry the JAK2 V617F mutation. The remaining roughly 5% have a different mutation in exon 12 of the same gene.
The test itself is straightforward: it requires only a regular blood sample, not a bone marrow sample. Results typically come back within one to two weeks. A positive JAK2 result in someone with elevated hemoglobin is strong evidence of PV, but the guidelines still require one more piece of the puzzle to make a formal diagnosis.
Erythropoietin Level
Erythropoietin (EPO) is a hormone your kidneys produce to tell bone marrow to make more red blood cells. In PV, the marrow is already overproducing on its own, so the body dials EPO production way down. A normal EPO level falls between roughly 2.6 and 18.5 mIU/mL. In PV patients, the average drops to about 3.4 mIU/mL, often landing below the normal range entirely.
By contrast, people whose red blood cell counts are high for other reasons (lung disease, sleep apnea, certain kidney tumors) tend to have elevated EPO levels, averaging around 23.7 mIU/mL. This makes the EPO test a useful way to separate PV from secondary causes of high red blood cell counts. A subnormal EPO level serves as the “minor criterion” in the WHO diagnostic framework, meaning it can help clinch a diagnosis when combined with elevated blood counts and a positive JAK2 test.
Bone Marrow Biopsy
A bone marrow biopsy is one of the three major diagnostic criteria. During this procedure, a needle is inserted into the back of the hip bone to withdraw a small core of marrow tissue. In PV, the marrow looks distinctly overcrowded: all three cell lines (red blood cells, white blood cells, and platelets) are overproduced at once, a pattern called panmyelosis. The platelet-producing cells, called megakaryocytes, also take on a characteristic appearance, appearing in varied sizes and shapes rather than the uniform look seen in healthy marrow.
These features help distinguish PV from situations where only red blood cells are elevated. A biopsy showing this three-way overgrowth pattern, combined with high hemoglobin and a JAK2 mutation, meets all three major criteria and confirms the diagnosis without needing an EPO level at all.
What to Expect During the Procedure
A bone marrow biopsy sounds more intimidating than it usually is. Most people receive local anesthesia at the biopsy site, though sedation through an IV is also an option. Special preparation isn’t typically needed, but if you’re receiving sedation, you’ll be asked to stop eating and drinking beforehand and arrange a ride home. Let your doctor know about any blood thinners, supplements like fish oil, or anti-inflammatory medications you take, since these can increase bleeding risk.
After the procedure with local anesthesia, you lie on your back for 10 to 15 minutes with pressure on the site, then go about your day. With IV sedation, expect to spend some time in a recovery area and take it easy for 24 hours. Keep the bandage dry for a day and avoid intense exercise for a day or two. Some tenderness at the site is normal and can last a week or longer.
How the Diagnostic Criteria Fit Together
The 2022 WHO guidelines lay out a clear formula. There are three major criteria: elevated hemoglobin or hematocrit above the thresholds, characteristic bone marrow findings, and a JAK2 mutation. There is one minor criterion: a subnormal EPO level. A diagnosis requires either all three major criteria, or the first two major criteria plus the minor criterion.
In practice, this means most people are diagnosed through blood work alone (hemoglobin plus JAK2 testing plus EPO level), with a bone marrow biopsy added to complete the picture. The biopsy also helps your doctor assess whether any scarring (fibrosis) has started in the marrow, which matters for long-term monitoring and treatment planning.
Tests That Are No Longer Standard
Older diagnostic approaches relied on directly measuring total red blood cell mass using radioactive tracers injected into the bloodstream. Research published in the journal Blood found that this test was neither diagnostically accurate nor essential in any of the cases studied. It has been largely replaced by the simpler combination of hemoglobin levels, JAK2 testing, and EPO measurement.
Physical Exam Findings
While not part of the formal diagnostic criteria, a physical exam can provide supporting clues. About 75% of PV patients have an enlarged spleen at the time of diagnosis, something your doctor can often feel during an abdominal exam. Around 30% also have an enlarged liver. A ruddy or reddish complexion, especially in the face and hands, is another common finding. None of these observations alone confirm PV, but they can prompt a doctor to order the right blood tests in the first place, particularly in someone whose blood counts are borderline.