In hematology, thrombocythemia is a condition of high platelet (thrombocyte) count in the blood. Normal count is in the range of 150×109 to 450×109 platelets per liter of blood, but investigation is typically only considered if the upper limit exceeds 750×109/L. When the cause is unknown, the term thrombocythemia is used, as either primary thrombocythemia or essential thrombocythemia...