Thrombocytosis is a condition in which there is an excessive number of platelets in the blood. Platelets are blood cells in plasma that stop bleeding by sticking together to form a clot. Too many platelets can lead to certain conditions, including stroke, heart attack, or a clot in the blood vessels.

There are two types of thrombocytosis: primary and secondary. Primary thrombocytosis, also known as essential thrombocythemia (or ET), is a disease in which abnormal cells in the bone marrow cause an increase in platelets. The cause is unknown. It is not considered an inherited (family) condition despite the finding of certain gene mutations in the blood or bone marrow.

Secondary thrombocytosis is caused by another condition the patient may be suffering from, such as:

  • Anemia due to iron deficiency
  • Cancer
  • Inflammation or infection
  • Surgery, especially splenectomy (removal of the spleen)

What are the symptoms of thrombocytosis?

Most patients do not experience any symptoms of an increased platelet count. When symptoms do appear, they can include skin bruising or bleeding from various areas such as the nose, mouth, and gums, or the stomach and intestinal tract.

Abnormal blood clotting can also occur, leading to stroke, heart attack, and unusual clots in the blood vessels of the abdomen.

Some patients with essential thrombocythemia develop erythromelalgia, causing pain, swelling, and redness of the hands and feet, as well as numbness and tingling.

How is thrombocytosis diagnosed?

Finding the underlying condition (such as iron deficiency anemia, cancer, or infection) can aid in the diagnosis and management of thrombocytosis. If no secondary cause is identified, the patient is presumed to have ET.

A blood test for a specific gene, called JAK2, can diagnose thrombocytosis. However, it is positive in only about 50% of the cases. Other gene mutations are also tested, but are only positive in a low percentage of patients.

The patient may have bone marrow removed and examined to help confirm the diagnosis.

How is thrombocytosis treated?

Patients who have no symptoms may remain stable and only require routine check-ups by their physician. Secondary forms of thrombocytosis rarely require treatment.

For those with symptoms, a few treatment options are available. One is to treat the disease that is causing thrombocytosis. In some cases, the patient can take aspirin to help prevent blood clots. The low dose used for this purpose does not usually cause stomach upset or bleeding.

In essential thrombocythemia, drugs such as hydroxyurea or anagrelide are used to suppress platelet production by the bone marrow. These drugs usually have to be taken indefinitely. Treatment with interferon is sometimes necessary but is associated with a greater number of side effects.

Newer agents are now being developed in an effort to suppress the overproduction of platelets. In cases of severe life-threatening thrombocytosis, a procedure called plateletpheresis is performed to immediately lower the platelet count to safer levels. In this procedure, a special instrument is used to remove blood from the patient, separate and remove the platelets, and then return the other blood cells to the patient.

What is the natural history of thrombocytosis?

Secondary thrombocytosis subsides when the underlying process causing the elevated platelet count resolves (treatment of infection, recovery from surgery, etc.). Even though the platelet count is elevated for a short time (or even indefinitely after splenctomy), secondary thrombocytosis does not typically lead to abnormal blood clotting.

Primary thrombocytosis, or essential thrombocythemia, can cause serious bleeding or clotting complications. These can usually be avoided by maintaining good control of the platelet count with medications. After many years, however, bone marrow fibrosis (scarring) can develop. Transformation of the disease to leukemia occurs in a small percentage of patients.


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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 10/25/2016...#13350