Thrombocytosis is a disorder in which your body produces too many platelets (thrombocytes), which play an important role in blood clotting. Also known as reactive thrombocytosis, the disorder can affect children and adults.

Reactive thrombocytosis occurs in response to an underlying condition. Thrombocytosis isn’t likely to cause symptoms.

Your treatment for thrombocytosis depends on the underlying condition that causes it. In most cases, your platelet count will return to normal after the condition is resolved.

Bone 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 (thrombi) to stop bleeding that occurs when you damage a blood vessel, such as when you cut yourself. A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood.

If you have thrombocytosis, your bone marrow overproduces the cells that form platelets (megakaryocytes), releasing too many platelets into your blood. If your blood test results show you have a high platelet count, it’s important for your doctor to determine whether you have thrombocythemia or reactive thrombocytosis to know how to treat your condition.

Reactive thrombocytosis causes include:

  • Infection
  • Recent surgery
  • Removal of your spleen
  • Cancer
  • Acute blood loss
  • Iron deficiency anemia
  • 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, connective tissue disorders or inflammatory bowel disease

Reactive thrombocytosis is rarely associated with symptoms. However, a high platelet count can be an indication of a serious bone marrow condition (also known as primary thrombocytosis or thrombocythemia), rather than of an underlying condition such as an infection. Thrombocythemia may put you at risk of developing blood clots, some of which can be life-threatening.

When to see a doctor
Because thrombocytosis is not likely to be associated with symptoms, you won’t know you have the condition unless a routine blood test reveals a high platelet count. Getting those test results will necessitate further consultation with your doctor.

It’s likely that a routine blood test that shows a high platelet count will be your first indication that you may 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 surgery, blood transfusions or infections you’ve had. He or she may refer you 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 due to an underlying condition (reactive thrombocytosis) or whether there’s no apparent cause, which could indicate thrombocythemia, a condition that increases your risk of developing blood clots.

Because appointments can be brief, and because there’s often a lot of ground to cover, it’s a good idea to be well prepared for your appointment. Here’s some information to help you get ready for your appointment, and 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.
  • Write down your health history, including recent infections or surgical procedures.
  • Write down key personal information, including any major stresses or recent life changes.
  • Make a list of all medications, as well as any vitamins or supplements, that you’re taking.
  • Take a family member or friend along, if possible. 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 questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out. For thrombocytosis, some basic questions to ask your doctor include:

  • What kinds of tests do I need?
  • Should I see a specialist? What will that cost, and will my insurance cover seeing a specialist?
  • Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you’ve prepared to ask your doctor, don’t hesitate to ask questions that arise during your appointment if you don’t understand something or need more information.

You may find out you have thrombocytosis through a routine blood test that shows you have a higher than normal platelet count. Or, if your doctor finds that your spleen is enlarged or if you have signs or symptoms of an infection or other condition, your doctor may order a complete blood count (CBC) to determine your platelet count. A blood smear, a test in which a small amount of your blood is examined under a microscope, helps determine the condition 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 600,000, then your doctor will look for an underlying condition. In most cases, signs and symptoms of the underlying condition help guide the diagnosis. However, in the case of cancer that has yet to be found, the diagnosis can be difficult.

Treatment of thrombocytosis is directed at the underlying cause. If the cause is a recent surgery or an injury that caused significant blood loss, your elevated platelet count may be short-lived. If the cause is a chronic infection or an inflammatory disease, your platelet count may remain high until the condition is brought under control.

Some procedures, such as removal of your spleen, may cause lifelong thrombocytosis. In that case, your doctor may prescribe low-dose aspirin to help prevent blood-clotting incidents, although they are rare with reactive thrombocytosis.