Thrombocytosis is a disorder in which your body produces too many platelets (thrombocytes), which play an important role in blood clotting. The disorder is called reactive thrombocytosis or secondary thrombocythemia when it’s caused by an underlying condition, such as an infection.
Thrombocytosis (throm-boe-sie-TOE-sis) may also, less commonly, be caused by a blood and bone marrow disease. When caused by a bone marrow disorder, thrombocytosis is called autonomous, primary or essential thrombocytosis, or essential thrombocythemia.
Your doctor may detect thrombocytosis in routine blood test results that show a high platelet level. If your blood test indicates thrombocytosis, it’s important to determine whether it’s reactive thrombocytosis or if you have essential thrombocythemia, which is more likely to cause blood clots.
Bone marrow — spongy tissue inside your bones — contains stem cells that can become red blood cells, white blood cells or platelets (thrombocytes). Platelets stick together, helping blood to form a clot that stops bleeding when you damage a blood vessel, such as when you get a cut. A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood.
If you have thrombocytosis caused by a bone marrow disorder (essential thrombocythemia), your bone marrow overproduces the cells that form platelets (megakaryocytes), releasing too many platelets into your blood. In essential thrombocythemia, there is a much higher risk of clotting or bleeding complications. Therefore, if your blood test results reveal a high platelet count, it’s important for your doctor to determine whether you have essential thrombocythemia or reactive thrombocytosis.
Reactive thrombocytosis causes include:
- Acute bleeding and blood loss
- Allergic reactions
- Chronic kidney failure or another kidney disorder
- Heart attack
- Coronary artery bypass
- Infections, including tuberculosis
- Iron deficiency
- Vitamin deficiency
- Removal of your spleen
Hemolytic anemia — a type of anemia in which your body destroys red blood cells faster than it produces them, often due to certain blood diseases or autoimmune disorders
- Inflammation, such as from rheumatoid arthritis, celiac disease, connective tissue disorders or inflammatory bowel disease
- Major surgery
Medications that can cause reactive thrombocytosis include:
- Epinephrine (AUVI-Q, EpiPen, others)
- Tretinoin (Retin-A, Renova, others)
- Vincristine Sulfate (Marqibo Kit)
- Heparin sodium
Reactive thrombocytosis rarely causes symptoms. More often, signs and symptoms relate to the underlying condition. If symptoms of reactive thrombocytosis do occur, they may include:
- Dizziness or lightheadedness
- Chest pain
- Temporary vision changes
- Numbness or tingling of the hands and feet
When to see a doctor
Because thrombocytosis isn’t likely to cause symptoms, you probably won’t know you have the condition unless a routine blood test reveals a higher than normal number of platelets. If your blood test results show a high platelet count, your doctor will try to determine the reason.