Platelet Disorders
Platelet Disorders

Platelet Disorders Thrombocythemia and Thrombocytosis

What are thrombocythemia and thrombocytosis?

What are they?

Thrombocythemia and thrombocytosis are conditions that occur when your blood has a higher-than-normal platelet count.

Platelets are tiny blood cells. They are made in your bone marrow along with other kinds of blood cells. When you are injured, platelets stick together to form a plug that seals your wound. This plug is called a blood clot. Platelets are also called thrombocytes,because a blood clot is also called a thrombus. If your platelet count is too high, blood clots can form in your blood vessels. This can block blood flow through your body.

  • Thrombocythemia refers to a high platelet count that is not caused by another health condition. This condition is sometimes called primary or essential thrombocythemia.
  • Thrombocytosis refers to a high platelet count caused by another disease or condition. This condition is often called secondary or reactive thrombocytosis. Thrombocytosis is more common than thrombocythemia.

What are the symptoms?


Many people who have thrombocythemia or thrombocytosis do not have symptoms. These conditions might be discovered only after routine blood tests.

The symptoms of a high platelet count are linked to blood clots and bleeding. These symptoms are more common in people who have thrombocythemia.

Blood clots

In thrombocythemia, blood clots most often develop in the brain, hands, and feet. But the clots can develop anywhere in the body. Blood clots in the brain may cause chronic (long-term) headaches and dizziness. In extreme cases, you may have a transient ischemic attack or a stroke.

You may have blood clots in the tiny blood vessels of your hands and feet. This can make your hands and feet numb and red. You may have a burning feeling and throbbing pain, mostly in the palms of the hands and the soles of your feet.

Other symptoms of a blood clot are:

  • Confusion or changes in speech
  • Migraines
  • Seizures
  • Upper body discomfort in one or both arms, your back, neck, jaw, or abdomen
  • Shortness of breath and nausea (feeling sick to your stomach)
  • Weakness
  • Chest pain
  • Pregnancy complications

You may also have a spleen that is larger than normal.

You may have a higher chance of a blood clot if you are older, have had blood clots in the past, smoke, or have other health conditions, such as diabetes and high blood pressure.


Bleeding can happen in people who have a very high platelet count. You may have nosebleeds, bruising, bleeding from your mouth or gums, or blood in your stool.

Bleeding occurs when blood clots that develop in thrombocythemia or thrombocytosis use up your body’s platelets. This means that not enough platelets are left in your bloodstream to seal off cuts or breaks on the blood vessel walls. Bleeding can also happen if your platelets do not work properly.

Another cause of bleeding in people who have very high platelets counts is a condition called von Willebrand disease. This condition affects how your blood clots. 

How are they diagnosed?


To diagnose thrombocythemia or thrombocytosis, your provider will ask about your medical and family history. They will ask about your symptoms and do a physical exam to look for signs of blood clots or bleeding.

Your provider may also order one or more of the tests below.

  • Complete blood count (CBC): A complete blood count (CBC) measures the levels of red blood cells, white blood cells, and platelets in your blood.
  • Blood smear: For this test, some of your blood is put on a slide. A microscope is used to look at your platelets and other blood cells.
  • Bone marrow tests: These tests check whether your bone marrow is healthy.
  • Genetic testing: This test checks for mutations, or changes, in genes that control how your body makes platelets.

What causes thrombocythemia?

Causes of thrombocythemia

Thrombocythemia occurs when faulty cells in your bone marrow make too many platelets. Your platelets also do not work properly. Bone marrow is the sponge-like tissue inside the bones. It contains stem cells that develop into platelets and other blood cells. With primary thrombocythemia, a high platelet count may happen alone or with other blood cell disorders. This condition is not common.

Thrombocythemia is most often caused by your genes. Mutations, or changes, in the genes that control how your bone marrow forms platelets may cause thrombocythemia. Examples of such genes include JAK2, CALR, and MPL. Thrombocythemia can be inherited. This means the condition can be passed from parents to children.

Primary thrombocythemia is more common in people ages 50 to 70, but it can occur at any age. It is more common in women than in men. 

What causes thrombocytosis?

Causes of thrombocytosis

Thrombocytosis occurs when another disease or condition causes you to have a high platelet count. People who have thrombocytosis have normal platelets and a lower risk of blood clots and bleeding than people who have thrombocythemia. Thrombocytosis is more common than thrombocythemia.

Some conditions that can raise your risk of thrombocytosis are listed below.

  • Anemia: Iron-deficiency anemia and hemolytic anemia can cause thrombocytosis.
  • Cancer: Many people who have high platelet counts also have cancer — mostly lung, gastrointestinal, breast, or ovarian cancer or lymphoma. Sometimes a high platelet count is the first sign of cancer.
  • Surgery to remove your spleen: The spleen is an organ in your upper left abdomen. Normally, your spleen stores platelets. Removing your spleen can raise your platelet count.
  • Inflammation or infections: Conditions such as connective tissue disorders, inflammatory bowel disease, and tuberculosis can raise your platelet count.

Your platelet count may be high for only a short time. This can be caused by:

  • Recovery from serious blood loss
  • Recovery from a very low platelet count caused by drinking too much alcohol and having low levels of vitamin B12 or folate
  • Acute (short-term) infection or inflammation

How are thrombocythemia and thrombocytosis treated?

Treatment and management

People who have thrombocythemia with no symptoms often do not need treatment. Other people who have this condition may need medicines or procedures to treat it. Treatment does not cure your condition, but it can help prevent blood clots and serious complications.

Treatment for secondary thrombocytosis depends on its cause. People who have thrombocytosis usually do not need platelet-lowering medicines or procedures. This is because their platelets are usually normal and less likely to cause serious blood clots or bleeding.

Treatment for thrombocythemia may include medicines and procedures.

Medicines to lower platelet counts

You may need one of the following medicines to lower your platelet count.

  • Anagrelide: This medicine is used to lower platelet counts. It is mostly used when hydroxyurea does not work. Anagrelide also has side effects, such as fluid retention, palpitations, arrhythmias, heart failure, and headaches.
  • Aspirin: This medicine helps prevent blood clots. It is mostly used in people who have a low risk of blood clots. If you have a high risk of blood clots, you may need to take both aspirin and hydroxyurea.
  • Hydroxyurea: This platelet-lowering medicine is used to treat cancers and sickle cell disease, for example.
  • Interferon alfa: This medicine lowers platelet counts, but it can have serious side effects. Side effects may include a flu-like feeling, decreased appetite, nausea (feeling sick to the stomach), diarrhea, seizures, irritability, and sleepiness.


Plateletpheresis is a procedure used to quickly lower your platelet count. This procedure is mostly used for emergencies. For example, if you are having a stroke due to primary thrombocythemia, you may need plateletpheresis.

An intravenous (IV) needle that is connected to a tube is placed in one of your blood vessels to remove blood. The blood goes through a machine that removes platelets from the blood. The remaining blood is then put back into you through an IV line in one of your blood vessels.

What health problems can thrombocythemia and thrombocytosis cause?

Health problems they can cause

Thrombocythemia and thrombocytosis may cause blood clots which can block blood flow to your organs. This can lead to the following serious complications:

Thrombocytopenia and thrombocytosis can also cause your bone marrow to become scarred or to produce too many blood cells. This may lead to some types of leukemia.

Learn how you can manage these platelet disorders to help avoid complications.

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