Thrombocytosis

When your blood has a number of platelets that is higher than normal, it is called thrombocythemia or thrombocytosis. There are two types: essential thrombocythemia and reactive thrombocytosis.

Essential thrombocythemia arises on its own, whereas reactive thrombocytosis is caused by another condition. The ‘essential’ type is also sometimes referred to as primary thrombocythemia, and the ‘reactive’ type is sometimes called secondary thrombocytosis.

This condition affects the platelets, which are tiny blood cells that are made in the bone marrow. They are important because when a blood vessel is damaged, they stick together forming a clot. This prevents excessive bleeding. Platelets are sometimes called thrombocytes because a blood clot is called a thrombus.

Thrombocytosis may be revealed in a blood test that shows high platelet count. A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. If a blood test has a platelet count higher than normal, it's important to find out if the condition is related to reactive thrombocytosis or essential thrombocythemia.

Thrombocytosis often has no signs or symptoms. The symptoms associated with reactive thrombocytosis are often simply the symptoms of the condition causing it.

Essential thrombocythemia sometimes has symptoms related to the effects blood clots and bleeding. These can include headaches, dizziness, chest pain, weakness, numbness, and tingling hands and feet. Because the platelets may not function properly, severe cases can cause visible bleeding, such as nosebleeds, bruising, bleeding gums and bloody stool.

Reactive thrombocytosis is more common than essential thrombocythemia. It is caused by an underlying condition, such as an infection. Compared to essential thrombocythemia, this type has a lower risk of complications.

Essential thrombocythemia is a type of blood condition called a chronic myeloproliferative disorder. This means that the bone marrow (the tissue inside bones that makes blood cells) overproduces one or more types of cell. In this case, the bone marrow makes too many platelets.

90% of people with essential thrombocytosis have acquired a gene mutation causing the condition. This is usually on the JAK2 gene, but can also be on the CALR gene, and rarely, the MPL, THPO, or TET2 genes. It is unclear how or why this mutation comes about and it means that there is no cure for the condition itself at present.

Normal platelet count is in the range of 150,000 to 450,000 platelets per microlitre of blood, but investigation is usually only considered if the number exceeds 750,000.

The higher the abnormal platelet count is, the higher the risk for abnormal bleeding and blood clots. If a blood clot occurs in the brain, this can cause a stroke, which can cause anything from temporary, mild impairment to long term brain injury.

Reactive thrombocytosis, or secondary thrombocytosis, is an acute biological response to an underlying condition such as an infection, but for example, can be associated directly with iron deficiency.

Conditions triggering increased platelet production can include acute blood loss, cancer, infections, iron deficiency, spleen removal, inflammatory disorder such as arthritis, and as a complication of surgery.

Reactive thrombocytosis is usually not a problem on its own, but can be indicative of a condition requiring investigation or treatment. Rarely, it may lead to blood clots or bleeding, but if the underlying cause is treated, any associated risk is unlikely to persist.

Reactive thrombocytosis is usually not considered to be serious. Unless you are suffering from signs or symptoms and so long as the associated condition stays stable, your doctor usually won’t prescribe treatment for it. If in doubt, ask your doctor or healthcare professional for guidance on whether your thrombocytosis needs to be managed.

Reactive thrombocytosis is usually managed by treating the underlying condition. For instance, if the reactive thrombocytosis is caused by anemia, once the anaemia is treated, the platelet count may return to normal.

Aspirin, which inhibits normal platelet clotting function (an ‘antiplatelet drug’), is often prescribed for those with thrombocytosis considered to be at risk of blood clots. Some people who have essential thrombocythemia may need other ongoing medication to lower their high platelet count.

Medications to treat high platelet count include hydroxyurea, anagrelide and interferon alfa. The most common treatment combination for patients with essential thrombocythemia who are at a high risk for blood clots is hydroxyurea plus an antiplatelet drug such as aspirin.