When to Worry About High Platelet Count

Platelets are the cells in the blood that help blood clot and help to plug the wall of a damaged blood vessel to prevent bleeding. Platelets are made in the bone marrow, which is inside the bones of the body.

The normal number of platelets is about 150,000 to 450,000 in a blood sample. Having a platelet level greater than 450,000 is called thrombocytosis.

Learn more about when to worry about high platelet count.

Activated platelets, artwork

SCIEPRO / Getty Images

Primary vs. Secondary Thrombocytosis

The two types of thrombocytosis are primary thrombocytosis and secondary thrombocytosis:

  • In primary thrombocytosis—also referred to as essential thrombocythemia—the high number of platelets being made is due to an abnormality in how the bone marrow is making them. A mutation may exist in the JAK2 gene, which causes an enzyme to work too much at making platelets. A mutation in the CALR gene can also cause too many platelets to be made in the bone marrow.
  • Secondary thrombocytosis can also be called reactive thrombocytosis, as the platelets rise in response to something outside of the bone marrow, such as an infection, inflammation, or bleeding.

High Platelet Count Isn’t Always Serious

Many times, a high platelet count doesn’t cause any symptoms but may be found on routine bloodwork. Although the cause for the high levels should be investigated, the possible cause is not always from something dangerous or serious.

Platelets can become elevated as a reaction to something else, such as an infection or inflammation, or due to iron deficiency. 

Potential Complications

Often people who have elevated platelets don’t have significant symptoms or complications. It is possible, however, that having high platelet counts can lead to the development of blood clots.

Blood clots can potentially form in any blood vessel, but most commonly form in the blood vessels in the arms and legs, or in the blood vessels in the brain. These clots can prevent blood from flowing properly through these vessels, and the decreased blood flow can cause complications.

If you have elevated platelets and are concerned about the risk of developing blood clots, talk to your healthcare providers about ways to reduce the risk of blood clots. 

Blood Conditions

Chronic myeloproliferative disorders are cancers of the blood in which too many blood cells are made. The myeloproliferative disorder that causes too many platelets to be made is called essential thrombocythemia, introduced above. This disorder is often the result of having a gene mutation in one of the JAK2, CALR, or MPL genes.

Essential thrombocythemia is not a common disease and is only diagnosed in about one in 100,000 people each year. 


One of the causes of secondary thrombocytosis can be cancer, and thrombocytosis can sometimes be a presenting symptom of cancer. The most common cancers to cause elevated platelets include ovarian cancer, gastrointestinal cancer, lung cancer, and breast cancer. 

What Healthcare Providers Look For

When evaluating the cause of elevated platelets, healthcare providers will be looking for signs or symptoms that may be present to help determine the cause. These symptoms may include:

  • Bruising
  • Bleeding
  • Stroke-like symptoms

It is likely that blood tests or imaging may be done. These tests may include:

  • Iron panel and ferritin, to show how much iron is present
  • Complete blood count, to evaluate full blood panel, including white blood cells and red blood cells
  • C-reactive protein, erythrocyte sedimentation rate blood tests, to check for markers that can show if inflammation is present
  • Blood testing, to check for JAK2, CALR, or MPL gene mutations
  • Bone marrow biopsy
  • Mammogram, to evaluate for the presence of breast cancer
  • Upper endoscopy and colonoscopy, to evaluate for the presence of gastrointestinal cancers
  • CT scan, MRI, or X-rays, to evaluate for the presence of cancer


Having elevated platelet counts can be associated with cancer, with one study reporting that about 11% of men with high platelets and about 6% of women with high platelets had cancer.

Though these may seem like significant numbers, it is important to remember that the majority of elevated platelet counts are caused by a reactive process, such as infection or inflammation. Once the cause of the reactive process resolves, platelet counts generally return to normal levels. 

Frequently Asked Questions

What does a high platelet count mean?

A high platelet count means that there are more platelets found in the blood than are typically found. Platelets are the blood cells that help blood clot and prevent bleeding.

What is considered a high platelet count?

A normal platelet count is between 150,000 to 450,000. A high platelet count is any number above 450,000.

What causes a high platelet count?

A high platelet count can be the result of a dysfunction in the bone marrow, or by a variety of other causes such as infection, inflammation, bleeding, or cancer.

How do you treat a high platelet count?

Treating high platelet counts starts with finding the cause of the high platelets and sometimes requires no treatment at all. If counts are elevated because of abnormal bone marrow, medications are available that slow down the production of platelets. Treating the cause of infection or inflammation may be all that is needed to decrease elevated platelets.

What cancers cause a high platelet count?

Cancers that may cause elevated platelets include:

Was this page helpful?
7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Medline Plus. Platelet disorders.

  2. MedlinePlus. Essential thrombocythemia. Updated May 2, 2021.

  3. Cleveland Clinic. Thrombocytosis. Updated March 2, 2021.

  4. National Heart, Lung and Blood Institute. Thrombocythemia and thrombocytosis.

  5. MedlinePlus. Essential thrombocythemia. Updated May 25, 2021.

  6. Watson J, Jones HE, Banks J, Whiting P, Salisbury C, Hamilton W. Use of multiple inflammatory marker tests in primary care: using Clinical Practice Research Datalink to evaluate accuracyBr J Gen Pract. 2019;69(684):e462-e469. doi:10.3399/bjgp19X704309

  7. Mounce LT, Hamilton W, Bailey SE. Cancer incidence following a high-normal platelet count: cohort study using electronic healthcare records from English primary care. Br J Gen Pract. 2020;70(698):e622-e628. doi:10.3399/bjgp20X710957