Thrombocythemia

Thrombocythemia
Other names	Thrombocytosis
3D rendering of four inactivated and three activated platelets
Specialty	Hematology

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,^[1] 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. The condition arises from a fault in the bone marrow cells leading to over-production of platelets but the cause of the fault is unknown, and this type is not common.^[2]

When the cause is known such as another disorder or disease, the term thrombocytosis is preferred, as either secondary or reactive thrombocytosis. Reactive thrombocytosis is the most common type and though it can often have no symptoms it can sometimes predispose to thrombosis. In contrast, thrombocytopenia refers to abnormally low blood platelet numbers in the blood.^[2]