Reactive thrombocytosis is an unusually high platelet count. Also known as secondary thrombocytosis, it results from an underlying health condition, an injury, or a medication.

Blood comprises plasma, red blood cells, white blood cells, and platelets. Each plays an important role in the health of the body.

For platelets, this contribution is helping the blood to clot. When high platelet counts are due to an injury, a health condition, or a medication, your doctor may diagnose reactive thrombocytosis. You may only discover that you have reactive thrombocytosis when your doctor does blood work.

If they discover that you have a high platelet count, they may recommend additional testing to rule out any serious underlying causes.

In most cases, addressing any health issues will normalize your platelet levels.

A typical platelet count is 150,000–450,000 per microliter (μL). When your platelet count exceeds 450,000/μL, you may have thrombocytosis.

Doctors typically divide thrombocytosis into two categories: reactive thrombocytosis and primary thrombocytosis. For proper treatment, it’s important for your doctor to determine which you have.

Reactive thrombocytosis, which is also known as secondary thrombocytosis, is an unusually high platelet count due to an underlying health condition, an injury, or the use of a medication.

An estimated 80–90% of people with thrombocytosis have reactive thrombocytosis.

Those with primary, or essential, thrombocytosis have a rare blood condition that causes the bone marrow to produce too many platelets. They have a higher risk of clots or bleeding.

You can read more about primary thrombocytosis here.

Causes of reactive thrombocytosis may include:

You don’t have a higher likelihood of developing reactive thrombocytosis based on your sex, age, or race.

Most people with reactive thrombocytosis don’t have any symptoms. Doctors often find the condition for the first time through simple lab work.

If you do experience any problems as a result of excess platelets in your blood, they may be related to a blood clot. Symptoms of a blood clot can include:

  • headaches or seizures
  • chest pain
  • weakness or dizziness
  • shortness of breath
  • pain in the arms, legs, hands, and feet
  • changes in speech

In rare cases, excess platelets can cause bleeding. This may appear in the form of:

  • nosebleeds
  • bruising
  • bloody stools
  • bleeding gums

Your doctor may prescribe medication to treat any underlying health conditions causing your elevated platelet levels. For example, they may prescribe iron supplements to help reduce platelet counts if you have inflammatory bowel disease.

If platelet levels are especially high or don’t improve as expected, your doctor might recommend a platelet-lowering medication. This isn’t usually necessary for thrombocytosis, but it can include taking:

If you have high platelet levels, your doctor may also recommend aspirin to help prevent blood clots.

Platelet-lowering medications can have side effects like nausea, dizziness, headaches, fluid retention, or sleepiness. You may wish to discuss these with your doctor before taking these medications.

While it’s not likely to be necessary, plateletpheresis is a procedure that can rapidly reduce the amount of platelets in your blood. Doctors tend to use it in emergency situations, like when a stroke occurs due to high blood platelet levels.

During plateletpheresis, blood exits the body through an intravenous (IV) tube, goes through a machine that removes platelets, and returns to the body through another IV line.

The platelet reduction accomplished by plateletpheresis isn’t a long-term solution or cure.

If your thrombocytosis causes a blood clot, you can experience serious complications like a stroke or heart attack.

If you’re pregnant, you may also experience pregnancy complications.

Reactive thrombocytosis rarely leads to a serious blood clotting problem. However, it can indicate that you have a serious condition like cancer. It’s important for your doctor to identify the underlying cause of your reactive thrombocytosis to determine how serious it is.

Your outlook with reactive thrombocytosis depends on the underlying cause.

While reactive thrombocytosis itself is typically a benign condition, you may have a poor outlook if it’s related to conditions like gastrointestinal cancer or chronic obstructive pulmonary disease.

If you have reactive thrombocytosis, it means you have an unusually high platelet count due to an underlying health condition, medication use, or an injury.

People with reactive thrombocytosis don’t often have symptoms, so you might not know you have it unless blood work reveals your higher platelet count.

Reactive thrombocytosis will typically resolve once a doctor addresses the underlying issue, but your outlook with the condition depends on its cause.

If your doctor determines that your platelet count is high, they may recommend additional testing to rule out health conditions like cancer.