What Causes Thrombocythemia and Thrombocytosis?

Primary Thrombocythemia

In this condition, faulty stem cells in the bone marrow make too many platelets. What causes this to happen usually isn't known. When this process occurs without affecting other blood cells, it's called essential thrombocythemia.

A rare form of thrombocythemia is inherited. ("Inherited" means the condition is passed from parents to children.) In some cases, a genetic mutation may cause the condition.

In primary thrombocythemia, the platelets aren't normal. They may form blood clots, or, surprisingly, cause bleeding when they don't work properly.

Bleeding also can occur because of a condition that develops called von Willebrand disease. This condition affects the blood clotting process.

After many years, scarring of the bone marrow can occur.

Secondary Thrombocytosis

This condition occurs when another disease, condition, or outside factor causes the platelet count to rise. For example, 35 percent of people who have high platelet counts also have cancer—mostly lung, gastrointestinal, breast, ovarian, and lymphoma. Sometimes a high platelet count is the first sign of cancer.

Unlike primary thrombocythemia, the platelets in secondary thrombocytosis usually are normal.

Conditions or factors that can cause a high platelet count are:

• Iron-deficiency anemia (uh-NEE-me-uh)
• Hemolytic (HEE-moh-lit-ick) anemia
• Absence of a spleen (after surgery to remove this organ)
• Cancer
• Inflammatory or infectious diseases such as connective tissue disorders, inflammatory bowel disease, and tuberculosis
• Reactions to medicines

Some conditions can lead to a high platelet count that lasts for only a short time. These include:

• Recovery from serious loss of blood
• Recovery from a very low platelet count caused by excessive alcohol use and lack of vitamin B12 or folate
• Acute infection or inflammation
• Response to physical activity