What Is Thrombocytosis?

Thrombocytosis is a condition characterized by an elevated platelet count in the blood.

Unlike red blood cells and white blood cells, platelets (also known as thrombocytes) are fragments of cells. Platelets work in tandem with other components of blood but are an essential part of the clotting process and wound healing.

When the platelet count exceeds the normal range, it can lead to a variety of health concerns. For example, as platelets are responsible for blood clotting, having an excess can greatly increase the risk of developing blood clots. In turn, these blood clots increase the likelihood of experiencing a pulmonary embolism.

Whether you have been diagnosed with thrombocytosis or are seeking more information about it, this article will provide valuable insights into the condition. Follow along to learn more about thrombocytosis and what you can do about it.

What Is Thrombocytosis?

The normal platelet count in an adult human ranges from 150,000 to 450,000 platelets per microliter of blood.

When platelet counts fall outside of this range, it can be diagnosed in one of three ways.


Thrombocytopenia is the opposite of thrombocytosis, as this condition occurs when the platelet count falls below 150,000 per microliter of blood.

Thrombocytopenia can be caused by various factors, including certain medications, autoimmune disorders, viral infections, and bone marrow disorders. It’s characterized by difficulty in clotting, which can lead to excessive blood loss.


Also known as essential thrombocythemia (ET), primary thrombocythemia, or essential thrombocytosis, this condition is characterized by a platelet count higher than 450,000 per microliter of blood.

Thrombocythemia occurs when the bone marrow produces an excessive number of platelets without any apparent underlying cause. It falls under the category of myeloproliferative neoplasms (MPNs), which involve abnormal growth and functioning of bone marrow cells.

Thrombocythemia is often associated with gene mutations, such as JAK2, CALR, or MPL, which disrupt the normal regulation of platelet production and lead to an elevated platelet count. Regular monitoring and appropriate management are necessary to reduce the risk of blood clots (known as thrombosis) from developing and contributing to additional complications.


Thrombocytosis, also referred to as secondary thrombocytosis, is also diagnosed when the platelet count surpasses the normal upper limit of 450,000 per microliter of blood. The difference is that this type of thrombocytosis occurs as a reactive response to an underlying condition or trigger.

Unlike primary thrombocythemia, thrombocytosis is not a medical condition itself but rather a consequence of an underlying condition. Therefore, the treatment of secondary thrombocytosis involves addressing the underlying cause.

What Causes Thrombocytosis?

While the cause of primary thrombocytosis is typically limited to genetic mutations in bone marrow cells, secondary thrombocytosis can have a variety of underlying causes and risk factors.

Inflammatory Conditions and Infections

Chronic inflammatory conditions like rheumatoid arthritis or inflammatory bowel disease can stimulate the production of platelets. Chronic inflammation triggers the release of cytokines, which in turn promotes platelet production.

Bacterial infections, especially severe or chronic ones, can also lead to reactive thrombocytosis as a response to the infection.

Iron Deficiency Anemia

Iron deficiency in the body can induce thrombocytosis as a compensatory mechanism. When the body lacks iron, it produces more platelets to help maintain blood clotting function.

Iron deficiency anemia can be caused by inadequate dietary intake, malabsorption issues, or chronic blood loss.

Cancer and Malignancies

Certain types of cancer and blood disorders, such as leukemia or lymphoma, can disrupt normal blood cell production in the bone marrow. The malignant cells crowd out healthy cells, leading to abnormal platelet production and thrombocytosis.

In cancer-related thrombocytosis, the underlying malignancy needs to be treated in order to address the elevated platelet count.


The spleen plays a crucial role in regulating platelet levels in the bloodstream. Surgical removal of the spleen, known as splenectomy, can result in an increased platelet count.

Without the spleen's regulatory function, platelets are not efficiently cleared from circulation, leading to thrombocytosis.

What Are the Symptoms of Thrombocytosis?

In many cases, thrombocytosis does not cause noticeable symptoms and is incidentally detected during routine blood tests. However, when symptoms do occur, they may include:

  • Thrombosis: Thrombosis (or blood clots) can partially or completely block blood vessels, leading to symptoms such as chest pain, shortness of breath, or pain and swelling in the legs.
  • Nosebleeds: You may experience spontaneous or frequent nosebleeds due to the increased fragility of blood vessels.
  • Easy bruising: The presence of an elevated platelet count can lead to easy bruising or the appearance of bruises with minimal trauma.
  • Excessive bleeding: Individuals with thrombocytosis may experience prolonged or excessive bleeding, especially from small cuts or injuries.
  • Fatigue and weakness: Fatigue and weakness can occur as a result of underlying anemia, which may accompany thrombocytosis in some cases.
  • Headaches and dizziness: These symptoms may occur due to impaired blood flow or the presence of blood clots in the blood vessels.

How Is Thrombocytosis Diagnosed?

Thrombocytosis is typically diagnosed through a comprehensive evaluation that involves several tests and assessments. These diagnostic measures aim to gather information about the platelet count, the characteristics of blood cells, and any underlying genetic mutations.

The following are commonly used diagnostic methods for thrombocytosis:

  • Complete blood count (CBC): A CBC is a standard blood test that provides essential information about the number and characteristics of different blood cells, including platelets.
  • Blood smear: A blood smear is a microscopic examination of a thin layer of blood. It allows for a closer evaluation of the blood cells' morphology, including platelets.
  • Bone marrow biopsy: In certain cases, a bone marrow biopsy may be performed to evaluate the production and characteristics of blood cells in the bone marrow.
  • Genetic testing: Genetic testing may be recommended, especially in cases of suspected primary thrombocythemia. Specific mutations, such as JAK2, CALR, or MPL, can be identified through genetic testing.

How Is Thrombocytosis Treated and Managed?

Once thrombocytosis is diagnosed, appropriate treatment and management strategies can be implemented to address the condition and minimize the risk of complications. The treatment and management of thrombocytosis depend on several factors, including the underlying cause, the severity of symptoms, and the risk of complications.

The following treatment options may be considered:

  • Observation: In cases where thrombocytosis is mild and not causing significant symptoms, your provider may suggest a strategy of close monitoring, also known as "watch and wait.”
  • Medications: Medications can be prescribed to help control platelet production and prevent the formation of blood clots. Commonly used medications for thrombocytosis include hydroxyurea, anagrelide, and interferon.
  • Plateletpheresis: In certain cases of severe thrombocytosis or when there is an urgent need to rapidly reduce the platelet count, plateletpheresis may be performed. This procedure can quickly lower the platelet count and alleviate symptoms.
  • Addressing underlying conditions: If thrombocytosis is secondary to an underlying condition, the primary focus of treatment is on managing and treating the underlying cause. This often involves collaborating with specialists in the respective fields, such as hematologists or oncologists, to develop a comprehensive treatment plan.

Any of these treatment methods require careful observation, and your healthcare provider will likely want to schedule regular follow-up appointments to monitor your progress. Make sure you follow their instructions and reach out to them if you have any questions or concerns, or if you notice any concerning symptoms.

The Bottom Line

Thrombocytosis is a serious condition that requires attention and appropriate management. By staying informed, seeking medical care, and utilizing available resources, you can navigate your journey with thrombocytosis more effectively.

If you or a loved one are living with thrombocytosis, Carda Health offers virtual services for cardiopulmonary rehab that can provide the support you need. Our healthcare professionals and clinical exercise physiologists specialize in in-home care and are experienced in managing cardiovascular and pulmonary conditions.

Explore our services today and take the first step towards supporting your health and well-being while dealing with thrombocytosis.


Platelet Disorders - Thrombocythemia and Thrombocytosis | NHLBI

Thrombocyte | ScienceDirect Topics

What Is a Normal Platelet Count? | OneBlood

Thrombocytopenia: Symptoms, Stages & Treatment | Cleveland Clinic

The Essential Thrombocythemia in 2020: What We Know and Where We Still Have to Dig Deep | NCBI Bookshelf

Thrombocytosis: Diagnostic Evaluation, Thrombotic Risk Stratification, and Risk-Based Management Strategies | PMC

Iron Deficiency Anemia - Symptoms & Causes | Mayo Clinic

Blood Cancers | Hematology.org

Postsplenectomy Reactive Thrombocytosis | PMC

Complete Blood Count (CBC) | MedlinePlus

Peripheral Blood Smear | NCBI Bookshelf

Genetic Testing | CDC

Plateletpheresis | ScienceDirect Topics

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