What is the difference between polycythemia and polycythemia vera?

September 29, 2025 •

5 min read

The term polycythemia is a general descriptor for a high red blood cell count, while polycythemia vera (PV) is a specific type of chronic blood cancer, characterized by this symptom. Understanding what is the difference between polycythemia and polycythemia vera is crucial for accurate diagnosis and management.

Quick Summary

Polycythemia is a broad medical term for any condition with an elevated red blood cell count, which can be caused by various factors including underlying diseases or low oxygen levels. Conversely, polycythemia vera is a specific, rare blood cancer caused by a genetic mutation that results in the overproduction of all blood cell types, not just red blood cells, within the bone marrow.

Key Points

Polycythemia is a general term: It refers to any condition resulting in a high red blood cell count, which can be either primary (intrinsic to the bone marrow) or secondary (caused by another medical condition).
Polycythemia vera is a specific cancer: This is a distinct type of chronic blood cancer, or myeloproliferative neoplasm, that is a form of primary polycythemia.
Cause is the main difference: PV is caused by an acquired JAK2 gene mutation, while secondary polycythemia results from factors like low oxygen or other diseases.
EPO levels differ: Patients with secondary polycythemia typically have normal or high erythropoietin (EPO) levels, whereas those with PV usually have low levels.
Treatment approaches vary: Secondary polycythemia is managed by addressing the underlying cause, while PV requires chronic management with treatments like phlebotomy, aspirin, and targeted drugs.
Potential for progression: Only polycythemia vera carries a risk of progressing to other serious blood disorders, such as myelofibrosis or leukemia.

Demystifying Polycythemia vs. Polycythemia Vera

The Broad Category: What Is Polycythemia?

Polycythemia, also known as erythrocytosis, literally means “many cells in the blood”. It is not a disease itself but rather a condition characterized by a higher-than-normal concentration of red blood cells in the bloodstream. This can cause the blood to thicken, slowing its flow and increasing the risk of complications such as blood clots.

There are two primary types of polycythemia:

Primary Polycythemia: This is caused by an intrinsic problem within the bone marrow itself, where the stem cells produce an excessive number of red blood cells. The most common form of primary polycythemia is Polycythemia Vera.
Secondary Polycycythemia: This is a more common type that occurs as a consequence of another underlying condition. The overproduction of red blood cells is typically a response to a physiological stimulus, often low oxygen levels (hypoxia). Common causes include:
- Living at high altitudes
- Chronic lung diseases, such as COPD
- Cyanotic heart disease
- Sleep apnea
- Certain kidney or liver diseases

The Specific Blood Cancer: What Is Polycythemia Vera?

Polycythemia Vera (PV) is a specific, rare blood cancer and a type of myeloproliferative neoplasm (MPN). It is a form of primary polycythemia, meaning the cause is intrinsic to the bone marrow. In over 95% of cases, PV is caused by an acquired genetic mutation in the Janus kinase 2 (JAK2) gene. This mutation causes the bone marrow's blood-forming stem cells to produce too many red blood cells, and often too many white blood cells and platelets as well.

Unlike secondary polycythemia, which is an increase in red blood cells that can be reversed by treating the underlying cause, PV is a chronic and progressive condition. Without treatment, it can be life-threatening. The extra blood cells can lead to a variety of symptoms and complications, including an enlarged spleen, blood clots, and in some rare cases, progression to more aggressive blood disorders like acute myeloid leukemia or myelofibrosis.

Distinguishing Symptoms and Manifestations

While both conditions can present with similar non-specific symptoms related to thickened blood, such as headaches, fatigue, and dizziness, certain signs and lab results can help differentiate between them.

Polycythemia (Secondary): Symptoms often correlate directly with the underlying cause, such as shortness of breath in a patient with a lung condition. Itchiness, particularly after a warm bath, is less common than in PV.
Polycythemia Vera (Primary): Symptoms can be more pronounced and may include:
- Intense, generalized itching (aquagenic pruritus) after exposure to warm water.
- Painful, burning sensation in the hands and feet (erythromelalgia).
- Early satiety or abdominal pain due to an enlarged spleen (splenomegaly).
- Unexplained weight loss and night sweats.

How Polycythemia and Polycythemia Vera Are Diagnosed

Diagnosing the specific condition is critical for proper treatment. The diagnostic process typically starts with a standard blood test, but further investigation is needed.

Initial Blood Tests: A complete blood count (CBC) will reveal an elevated hemoglobin or hematocrit level in both conditions. In PV, there may also be an increase in white blood cells and platelets.
Erythropoietin (EPO) Levels: This is a key differentiating test. In secondary polycythemia, EPO levels are typically normal or high, as the body is responding to a lack of oxygen. In PV, EPO levels are often very low because the bone marrow is overproducing cells independently of the normal signals.
Genetic Testing: Testing for the JAK2 gene mutation is a definitive diagnostic tool for PV.
Bone Marrow Biopsy: A biopsy may be performed to examine the bone marrow's cellularity. In PV, it shows a specific pattern of proliferation across all three blood cell lines.

Comparison of Polycythemia and Polycythemia Vera


Feature	Polycythemia (General)	Polycythemia Vera (PV)
Classification	A broad term for high red blood cell count.	A specific type of primary polycythemia; a chronic blood cancer.
Underlying Cause	Often secondary to another medical condition (e.g., hypoxia from lung disease).	Caused by an acquired JAK2 gene mutation in over 95% of cases.
Driver of RBC Production	High erythropoietin (EPO) levels as a response to low oxygen.	Intrinsic bone marrow defect, independent of EPO levels.
Blood Cell Lines Affected	Primarily elevated red blood cells.	Excessive production of red blood cells, white blood cells, and platelets.
Erythropoietin (EPO) Level	Normal or high.	Typically low.
Genetic Mutation	Not associated with the JAK2 mutation.	Defined by the presence of a JAK2 mutation.
Complications	Mainly related to blood thickness and hyperviscosity.	Increased risk of blood clots, enlarged spleen, progression to myelofibrosis or leukemia.
Treatment Focus	Addressing the underlying cause (e.g., managing lung disease).	Chronic management with phlebotomy, low-dose aspirin, and potentially targeted medications (e.g., ruxolitinib).

Treatment Approaches for Both Conditions

Treatment differs significantly based on the diagnosis.

Treatment for Secondary Polycythemia: The main goal is to treat the underlying condition. For instance, if the cause is sleep apnea, treating that will resolve the polycythemia. Smoking cessation is also a critical step.
Treatment for Polycythemia Vera: PV is a chronic condition that requires ongoing management. Key treatments include:
- Phlebotomy: Regular removal of blood to reduce the volume and thickness, lowering the hematocrit to a target level.
- Medication: Low-dose aspirin is often prescribed to reduce the risk of blood clots. In higher-risk patients, or those with severe symptoms, medications like hydroxyurea or ruxolitinib may be used to suppress bone marrow production.
- Symptom Management: Therapies for itching (pruritus) may involve specific medications or UV light treatment.

Seeking Expert Medical Advice

Navigating the nuances of polycythemia and polycythemia vera underscores the importance of a proper medical evaluation. Due to the potential for serious complications like blood clots and the risk of progression in PV, it is crucial to consult with a hematologist to confirm the diagnosis and develop a personalized treatment plan. For further reading on blood-related conditions, a reliable resource can be found at the National Heart, Lung, and Blood Institute website.

Conclusion: A Clear Distinction for Proper Care

In summary, while both polycythemia and polycythemia vera involve an elevated red blood cell count, they are fundamentally different in their cause and nature. Polycythemia is a general term often secondary to other factors, whereas PV is a specific, chronic blood cancer rooted in a genetic mutation within the bone marrow. The distinction dictates the appropriate diagnostic and therapeutic approach, emphasizing the importance of expert medical consultation for anyone with high red blood cell counts.

Frequently Asked Questions

No, secondary polycythemia cannot progress into polycythemia vera. Secondary polycythemia is a reactive condition caused by an external factor, whereas PV is a separate, clonal disorder caused by a genetic mutation within the bone marrow itself.

There is an overlap in general symptoms like headaches and fatigue, but PV often presents with specific, pronounced symptoms, such as severe itching after warm water exposure (aquagenic pruritus) and painful, burning hands and feet (erythromelalgia).

Measuring the level of erythropoietin (EPO) is a key test. Low EPO levels suggest PV, while normal or high levels point towards a secondary polycythemia. Genetic testing for the JAK2 mutation is also definitive for PV.

No, many people with polycythemia vera have no noticeable symptoms for years, and the condition is often discovered during routine blood tests. Symptom severity can vary greatly from person to person.

For secondary polycythemia, treatment focuses on resolving the underlying cause. For polycythemia vera, the approach is chronic management, including phlebotomy, low-dose aspirin, and potentially other medications to control blood cell counts.

The JAK2 mutation is a genetic change that occurs in the blood-forming stem cells of the bone marrow. In PV, this mutation signals the cells to produce blood cells excessively, even without external stimulation from hormones like EPO.

For secondary polycythemia caused by lifestyle factors like smoking, quitting is crucial. For PV, a healthy lifestyle is important for overall cardiovascular health, which helps mitigate the risks associated with the disease.