Because polycythemia vera (PV) is a rare type of blood cancer, a diagnosis often comes when you see your doctor for other reasons.

To diagnose PV, your doctor will do a physical examination and blood test. They may also perform a bone marrow biopsy.

A diagnosis of PV is usually not the result of a physical exam. But your doctor may observe symptoms of the disease during a routine visit.

Some physical symptoms your doctor may recognize are bleeding gums and a reddish hue to your skin. If you have symptoms or your doctor suspects PV, they will most likely examine and palpate your spleen and liver to determine if they’re enlarged.

There are three main blood tests that are used to diagnose PV:

Complete blood count (CBC)

A CBC measures the number of red and white blood cells and platelets in your blood. It will also tell your doctor what your hemoglobin level is in your bloodstream.

Hemoglobin is a protein rich in iron that helps red blood cells carry oxygen from the lungs to the rest of the body. And if you have PV, your hemoglobin level will be elevated. Usually, the more red blood cells you have, the higher your hemoglobin level.

In adults, a hemoglobin level greater than 16.0 grams per deciliter (g/dL) in women or 16.5 g/dL in men can indicate PV.

A CBC will also measure your hematocrit. Hematocrit is the volume of your blood that’s made up of red blood cells. If you have PV, a higher-than-normal percentage of your blood will be made of red blood cells. In adults, a hematocrit greater than 48 percent in women or greater than 49 percent in men can indicate PV, according to the World Health Organization.

Blood smear

A blood smear looks at your blood sample under a microscope. This can show the size, shape, and condition of your blood cells. It can detect abnormal red and white blood cells, along with platelets, that can be linked to myelofibrosis and other bone marrow problems. Myelofibrosis is serious bone marrow scarring that can develop as a complication of PV.

Erythropoietin test

Using a blood sample, an erythropoietin test measures the amount of the hormone erythropoietin (EPO) in your blood. EPO is made by the cells in your kidneys and signals stem cells in the bone marrow to make more red blood cells. If you have PV, your EPO level should be low. This is because your EPO isn’t driving blood cell production. Instead, a JAK2 gene mutation is driving blood cell production.

Bone marrow tests can determine if your bone marrow is making normal amounts of blood cells. If you have PV, your bone marrow is making too many red blood cells, and the signal to make them doesn’t turn off.

There are two main types of bone marrow tests:

During a bone marrow aspiration, a small amount of the fluid part of your bone marrow is removed with a needle. For a bone marrow biopsy, a small amount of the solid part of your bone marrow is removed instead.

These bone marrow samples are sent to a lab for analysis by either a hematologist or a pathologist. These specialists will analyze the biopsies and send your doctor the results within a few days.

The discovery of the JAK2 gene and its mutation JAK2 V617F in 2005 was a breakthrough in learning about PV and being able to diagnose it.

About 95 percent of people with PV have this genetic mutation. Researchers have found that JAK2 mutations also play an important role in other blood cancers and platelet problems. These diseases are known as myeloproliferative neoplasms (MPNs).

The genetic abnormality can be detected in both your blood and your bone marrow, requiring either a blood sample or a bone marrow sample.

Because of the discovery of the JAK2 gene mutation, doctors can more easily diagnose PV with a CBC and a genetic test.

Although PV is rare, getting a blood test is one of the best ways to get an early diagnosis and treatment. If your doctor determines that you do have PV, there are ways of managing the disease. Your doctor will make recommendations based on your age, the progression of the disease, and your overall health.