When to Worry About High Platelet Count

A high platelet count is not always a serious concern

When you have more platelets in your blood than you should, it's known as thrombocytosis, or a high platelet count. Platelets are small blood cells that help form clots to prevent bleeding.

It's natural to worry about high platelet levels, just like you might any other abnormal blood test result. But while they may indicate an underlying condition, a high platelet count is not always due to something serious.

This article explains what may cause a high platelet count. It will also cover potential complications, how its cause is diagnosed, and treatment options.

What Is the Difference Between Primary and Secondary Thrombocytosis?

Platelets, also called thrombocytes, are the cells in the blood that help blood clot. Clotting plugs the wall of a damaged blood vessel to prevent bleeding. Platelets are made in the bone marrow, which is the spongy tissue inside the bones of the body.

The normal number of platelets is about 150,000 to 450,000 per microliter of blood. Having a platelet level greater than 450,000 is considered thrombocytosis.

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

  • In primary thrombocytosis—also called essential thrombocythemia—the bone marrow makes too many platelets. This may be caused by mutations, or genetic changes, in two specific genes, the JAK2 gene and the CALR gene.
  • Secondary thrombocytosis, also called reactive thrombocytosis, occurs when the platelets increase in response to a condition, infection, medications, or bleeding.

Is High Platelet Count Always Serious?

Many times, a high platelet count doesn’t cause any symptoms. It may just be found through routine blood work.

Although the cause for the high levels should be investigated, it is not always due to something dangerous or serious. For example, platelets can become elevated in response to medications, an infection, low iron levels, or exercising. 

What Are Some Potential Complications?

Potential Complications From High Platelet Count - Illustration by Theresa Chiechi

Verywell / Theresa Chiechi

Often, people who have elevated platelets don’t have any complications. However, some who have high platelet counts experience blood clots.

Blood clots may form in any blood vessel. Most commonly, they form in the blood vessels in the arms and legs, or in the brain. These clots can prevent blood from flowing properly through these vessels. This decreased blood flow can cause symptoms including:

  • Headaches
  • Dizziness
  • A stroke, which is a medical emergency that occurs when a clot blocks the flow of blood and oxygen to the brain
  • Throbbing pain or numbness
  • A seizure, which is a medical emergency that occurs when the brain cells suddenly have too much activity

If you have elevated platelets and are worried about the risk of developing blood clots, talk to your healthcare provider. 

High Platelets in Pregnancy and Children

Platelet counts usually drop slightly during pregnancy without a problem. However, sometimes platelet levels can become too low—or too high. In some cases this is due to a problem that existed prior to pregnancy; in others, it comes on during pregnancy.

A very high platelet count can cause blood clots that can block blood flow to the baby, while low platelet counts can cause bleeding.

Complications that can be a result of either too high or too low platelet levels include:

  • High blood pressure
  • Slow fetal growth
  • Premature delivery
  • Separation of the placenta from the womb
  • Miscarriage

In most cases, platelet levels can be managed by getting routine medical care during pregnancy. If platelet levels are too high, it may be necessary to take anti-clotting medications until the baby is safely delivered. Delivering the baby early may also be recommended.

Pre-term infants are often born with high platelet counts. In most cases, this is not serious and resolves on its own a few weeks after birth. In older children, high platelet counts are usually a result of infection and also resolve once the infection passes.


High platelets are sometimes associated with certain kinds of cancer, including:

Blood Cell Cancer

Essential thrombocythemia has the potential to turn into a type of blood cell cancer known as acute leukemia. Keep in mind that this is very rare. 

Other Cancers

One of the causes of secondary thrombocytosis can be cancer. Thrombocytosis can sometimes be one of the first symptoms of cancer.

The most common cancers to cause elevated platelets include ovarian cancer, lung cancer, and breast cancer. Elevated platelets can also be seen in gastrointestinal cancer, which refers to cancer anywhere in the digestive tract, as well as lymphoma, which is cancer found in the vessels that carry fluid from tissues and cells throughout the body. 

What Do Healthcare Providers Look For?

When evaluating the cause of elevated platelets, healthcare providers may look for symptoms like bruising, bleeding, and signs of infection or another underlying condition.

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

  • Iron panel to show how much iron is present
  • Complete blood count, which is a full blood panel that includes white blood cell and red blood cell count
  • C-reactive protein and erythrocyte sedimentation rate blood tests to see if inflammation is present, which would indicate if the body is trying to heal from an infection or injury
  • Blood testing to check for specific gene mutations
  • Bone marrow biopsy, which removes a sample of bone marrow for evaluation
  • Mammogram, an imaging test that checks for breast cancer
  • Upper endoscopy, which is a procedure that inserts a small tube with a camera into the mouth and down to the stomach, to check for cancer in the upper digestive tract
  • Colonoscopy, which is a procedure that uses a small tube with a camera that is inserted into the rectum to check for gastrointestinal cancer in the large intestine

How Do You Treat a High Platelet Count?

Treating a high platelet counts starts with finding the underlying cause. In some cases, if there are no symptoms, no treatment may be required.

Treatment for essential thrombocythemia may include certain medications that slow down the production of platelets. In secondary thrombocytosis, treating the underlying condition, like an infection, may be all that is needed to decrease elevated platelets.

What Is the Outlook for Those With High Platelet Counts?

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

Remember that the majority of elevated platelet counts are caused by a reactive process, such as infection or inflammation. Once the underlying cause resolves, platelet counts generally return to normal levels. 


Having elevated platelet levels, or thrombocytosis, doesn't always indicate something serious is going on. Sometimes high platelet levels are triggered by an infection, medications, low iron levels, or physical activity.

Having high platelets doesn't always cause symptoms, but some may experience complications such as blood clots. High platelets may also point to certain kinds of cancer.

Treatment for elevated platelet levels will vary depending on the underlying cause.

Frequently Asked Questions

  • What is considered a high platelet count?

    A high platelet count is when you have more than 450,000 platelets per microliter of blood. Platelet counts can rise temporarily, so your healthcare provider may want to re-test you after a period of time to see if they are still high.

  • What causes a high platelet count?

    Sometimes, your body simply makes too many platelets. In other cases, there may be a problem like an infection or anemia. Because some of these problems can be serious, high platelets always need to be thoroughly evaluated by a healthcare provider.

  • What infections cause high platelets?

    Research has found that urinary tract infections, respiratory infections, and gastrointenstinal infections are among the leading causes of thrombocytosis (high platelet count).

  • Does COVID affect platelet count?

    Yes. Inflammatory proteins produced as a result of COVID-19 infection significantly raise platelet counts and the risk of forming dangerous blood clots. This can lead to heart attacks, strokes, and other serious complications.

  • What cancers cause a high platelet count?

    High platelets don't always point to cancer, but researchers think they may be able to help diagnose certain cancers including lung, colorectal, breast, and prostate cancers.

  • Can stress cause high platelets?

    Yes. Studies have found that stress can result in higher platelet levels.

11 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.
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By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.