Understanding the Connection: Does Polycythemia Vera Have Thrombocytosis?

October 1, 2025 •

3 min read

While polycythemia vera is primarily known for an overproduction of red blood cells, studies show that an excess of platelets, a condition known as thrombocytosis, is also very common and occurs in at least half of all cases. This abnormal increase in blood cells is a hallmark of this rare blood cancer and plays a significant role in its associated complications.

Quick Summary

Polycythemia vera frequently involves thrombocytosis, an elevated platelet count, in addition to increased red blood cells. This can increase the risk of blood clots and bleeding and requires careful management. Both conditions stem from a common genetic mutation affecting hematopoietic stem cells.

Key Points

Yes, PV includes thrombocytosis: Polycythemia vera often involves an overproduction of platelets, a condition called thrombocytosis, in addition to its defining feature of excess red blood cells.
JAK2 mutation is the cause: The underlying JAK2 gene mutation in most PV patients drives the uncontrolled proliferation of hematopoietic stem cells, leading to an increase in red cells, white cells, and platelets.
Thrombocytosis increases health risks: Elevated platelet counts in PV raise the risk of both blood clots and, paradoxically, bleeding problems, especially with very high platelet levels.
Causes microvascular symptoms: Thrombocytosis can cause microcirculatory symptoms like erythromelalgia (painful burning in hands/feet), headaches, and visual disturbances.
Treatment involves controlling all cell counts: Management of PV, particularly in high-risk patients, requires controlling elevated platelet counts using cytoreductive therapies like hydroxyurea and low-dose aspirin to prevent complications.

Polycythemia vera (PV) is a chronic blood cancer originating in the bone marrow. It is characterized by an overproduction of blood cells, most notably red blood cells, but often includes white blood cells and platelets as well. This overproduction of platelets is known as thrombocytosis and is a common feature in many PV patients.

The Pathophysiology: Why Polycythemia Vera Causes Thrombocytosis

The primary cause of polycythemia vera and the associated thrombocytosis is a genetic mutation.

The Role of the JAK2 Gene Mutation

Over 95% of PV cases are linked to a mutation in the Janus kinase 2 (JAK2) gene, frequently the JAK2V617F mutation. This mutation leads to continuous signaling within hematopoietic stem cells, causing uncontrolled blood cell production. The mutated stem cells are less reliant on normal growth factors, resulting in an overproduction of red blood cells, white blood cells, and megakaryocytes, which produce platelets. This can even cause thrombocytosis to appear before erythrocytosis in some cases.

Thrombocytosis in PV vs. Essential Thrombocythemia (ET)

Thrombocytosis can occur in both PV and Essential Thrombocythemia (ET), another myeloproliferative neoplasm (MPN), and distinguishing between them is important for diagnosis and management.

Comparison of Thrombocytosis in PV and ET


Feature	Thrombocytosis in Polycythemia Vera (PV)	Thrombocytosis in Essential Thrombocythemia (ET)
Primary Cell Line Affected	Red blood cells are the most elevated component, leading to thickened blood and hyperviscosity.	Platelets are the primary cell line that is overproduced.
Other Cell Lines	Often includes elevated white blood cells and platelets, a condition known as panmyelosis.	Typically features an isolated elevation of platelets, though other cell lines may sometimes be affected.
Driver Mutations	Over 95% of patients have a JAK2 mutation (JAK2V617F or JAK2 exon 12).	Mutations in JAK2, CALR, or MPL are common but mutually exclusive. A significant number are "triple negative".
Diagnostic Challenges	Diagnosis can be complex, especially in early stages where platelet elevation may be more prominent or if hemoglobin levels are masked by iron deficiency.	Diagnosis requires excluding other MPNs and reactive causes of thrombocytosis.
Bleeding Risk	Extreme thrombocytosis (>1,000 x 10^9/L) can lead to acquired von Willebrand syndrome, causing a paradoxical bleeding risk.	Extreme thrombocytosis is also a risk factor for acquired von Willebrand syndrome and bleeding in ET.

Signs and Symptoms of Thrombocytosis in PV

Thrombocytosis in polycythemia vera can manifest through various symptoms, often related to microvascular circulation. These can include painful burning and redness in the hands and feet (erythromelalgia), headaches, dizziness, and visual disturbances due to reduced blood flow and increased viscosity. Elevated platelets, combined with increased red blood cells, also significantly raise the risk of serious blood clots, such as DVT, stroke, or heart attack.

Managing Thrombocytosis in Polycythemia Vera

Managing PV involves controlling both red blood cell counts and thrombocytosis to mitigate complications. Low-dose aspirin is often prescribed to reduce clot risk by affecting platelet function, but caution is needed in cases of extremely high platelet counts due to potential bleeding risk. Cytoreductive therapies like hydroxyurea or interferon-alpha are used in high-risk patients or those with significant symptoms to reduce blood cell production. Ruxolitinib, a JAK1/JAK2 inhibitor, may be used if other treatments are ineffective. While phlebotomy helps manage red blood cell volume, it doesn't directly address thrombocytosis.

For more detailed information on polycythemia vera treatments, refer to the American Society of Hematology's comprehensive review on the topic [ashpublications.org/hematology/article/2017/1/480/21108/What-are-the-current-treatment-approaches-for].

Conclusion

In conclusion, polycythemia vera frequently involves thrombocytosis, an elevation in platelet count, in addition to increased red blood cells. This is primarily caused by the underlying JAK2 gene mutation, leading to the overproduction of multiple blood cell types. This elevated platelet count contributes to increased risk of blood clots and, in extreme cases, paradoxical bleeding. Effective management of PV requires addressing all abnormal cell counts to reduce associated health risks.

Frequently Asked Questions

Thrombocytosis is a common feature of polycythemia vera, stemming from the same underlying genetic mutation that causes the overproduction of red blood cells. It can be viewed as a manifestation of the disease rather than a secondary complication, although it significantly contributes to the risk of complications.

The JAK2 mutation activates the Janus kinase signaling pathway in hematopoietic stem cells. This causes a constant, unregulated proliferation of all myeloid blood cell lineages, including megakaryocytes which produce platelets, even without normal growth factor stimulation.

Yes, in a seemingly paradoxical manner, extremely high platelet counts (typically over 1,000 x 10^9/L) in PV can lead to bleeding. This is because the excess platelets can bind and inactivate von Willebrand factor, a crucial protein for blood clotting, resulting in an acquired von Willebrand syndrome.

In polycythemia vera, thrombocytosis is one aspect of a wider overproduction of blood cells (panmyelosis), with erythrocytosis being the most prominent feature. In contrast, essential thrombocythemia is primarily defined by the isolated, chronic overproduction of platelets.

Management often includes low-dose aspirin to reduce the risk of clotting. For high-risk patients or those with severe symptoms, cytoreductive therapies like hydroxyurea or interferon are used to lower the overall number of blood cells, including platelets.

While phlebotomy is highly effective for reducing red blood cell volume and blood viscosity, it does not reliably control thrombocytosis. Therefore, separate measures, such as cytoreductive therapy, are often necessary to manage high platelet counts.

Symptoms of thrombocytosis in PV can include erythromelalgia (painful burning and redness in the hands or feet), headaches, dizziness, and visual disturbances, all of which are related to microvascular dysfunction caused by abnormal platelets.