I saw the following comment and it may help you understand this condition further :
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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. Platelets are also called thrombocytes, because a blood clot is also called a thrombus.

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.