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Causes
By Mayo Clinic staffBone marrow — spongy tissue inside your bones — contains stem cells that can become red blood cells, white blood cells or platelets. Platelets travel through your blood vessels. They stick together to form clots to stop bleeding that occurs when you damage a blood vessel, such as when you experience a cut. A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood.
If you have thrombocythemia, your bone marrow overproduces the cells that form platelets (megakaryocytes), releasing too many platelets into your blood. The overproduced platelets may not function normally, leading to abnormal clotting or bleeding.
The cause of thrombocythemia isn't well understood. Some people with the disorder have a mutation of the Janus kinase 2 (JAK2) gene in their blood cells, but having the mutation doesn't appear to affect the course of the disease, so its exact role is unknown. A rare form of thrombocythemia is inherited. Generally, if you receive a diagnosis of thrombocythemia, the cause isn't known.
In some cases, an underlying condition, such as cancer, removal of the spleen, rheumatoid arthritis or iron deficiency anemia, may cause the overproduction of platelets. Then the disorder is known as thrombocytosis.
