Medically reviewed on April 7, 2018
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.
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.
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
- Coronary artery bypass
- Heart attack
- 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
- Infections, including tuberculosis
- Inflammation, such as from rheumatoid arthritis, celiac disease, connective tissue disorders or inflammatory bowel disease
- Iron deficiency
- Major surgery
- Removal of your spleen
- Vitamin deficiency
Medications that can cause reactive thrombocytosis include:
- Epinephrine (AUVI-Q, EpiPen, others)
- Tretinoin (Retin-A, Renova, others)
- Vincristine Sulfate (Marqibo Kit)
- Heparin sodium
You may find out you have thrombocytosis through one of the following tests:
- A routine blood test. This test may show a higher than normal platelet count.
- During a physical exam. If your doctor finds that your spleen is enlarged or you have signs or symptoms of an infection or another condition, he or she may order a complete blood count (CBC) to determine your platelet count.
- A blood smear. Your doctor may examine a small amount of your blood under a microscope to view the size and activity of your platelets.
Because a number of conditions can cause a temporary rise in your platelet count, your doctor likely will repeat the blood tests to see if your platelet count remains high over time.
A normal range for platelets is 150,000 to 450,000 platelets per microliter of blood. If your blood count is above 450,000, your doctor will likely look for an underlying condition. In most cases, signs and symptoms of the underlying condition help guide the diagnosis. Your doctor may also:
- Check the level of iron in your blood
- Test for markers of inflammation
- Order genetic testing to help determine if you have a blood and bone marrow disorder such as essential thrombocythemia
- Conduct a bone marrow aspiration and biopsy to collect and examine bone marrow tissue
Treatment for reactive thrombocytosis is directed at the underlying cause. If a recent surgery or an injury that caused significant blood loss is the cause, your elevated platelet count may not last long. If the cause is a chronic infection or an inflammatory disease, your platelet count may remain high until the condition is brought under control. In most cases, your platelet count will return to normal after the underlying cause is resolved.
If you have reactive thrombocytosis, it is unlikely that you will need drugs or a medical procedure to lower your platelet count. It is also unlikely that you will experience blood clotting or bleeding.
Removal of your spleen (splenectomy) may cause lifelong thrombocytosis, but you are unlikely to need treatment.
Preparing for an appointment
It's likely that a routine blood test showing a high platelet count will be your first indication that you have thrombocytosis.
Besides taking your medical history, examining you physically and running tests, your doctor may ask you about factors that could affect your platelets, such as any recent surgical procedures, blood transfusions or infections. You may be referred to a doctor who specializes in blood diseases (hematologist).
Your doctor will look for what's causing your high platelet count, including determining whether it's reactive thrombocytosis due to an underlying condition or whether there's no apparent cause, which could indicate essential thrombocythemia or another bone marrow disorder.
Here's some information to help you get ready and to know what to expect from your doctor.
What you can do
- Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance, such as restrict your diet.
- Write down any symptoms you're experiencing, including any that may seem unrelated to the reason you are scheduling your appointment.
- Write down your health history, including recent infections, surgical procedures, bleeding and anemia.
- Make a note of key personal information, including things like recent life changes, or major stresses.
- Make a list of all medications, vitamins and supplements that you're taking.
- Take a family member or friend along. Sometimes it can be difficult to take in all the information you hear during an appointment. Someone who accompanies you may remember something that you missed or forgot.
- Write down a list of questions to ask your doctor.
For thrombocytosis, some basic questions to ask include:
- What kinds of tests do I need?
- Is my condition temporary or chronic?
- What treatment do you recommend?
- Will I need to take medication?
- Will I have any side effects from the treatment?
- What kind of follow-up will I need?
- Do I need to restrict my activity?
- What are possible complications of my condition?
- I have other health conditions. How can I best manage them together?
- Should I see a specialist?
- Do you have any brochures or other printed material that I can take with me?
- What websites do you recommend?
Don't hesitate to ask other questions that occur to you during your appointment.
What to expect from your doctor
Examples of questions your doctor may ask, include:
- What signs and symptoms have you noticed?
- When did you first notice these signs and symptoms?
- Have they gotten worse over time?
- Have you had a recent medical procedure or blood transfusion?
- Have you had a recent infection or vaccine?
- Do you drink alcohol?
- Do you have headaches, dizziness or weakness?
- Do you have any chest pain?
- Have you had any vision problems?
- Have you had any bleeding or bruising?
- Have you experienced any numbness or tingling in your hands or feet?
- Do you have a family history of high platelet counts?