What is Thrombocytosis?

Thrombocytosis (throm-bo-sigh-TOE-sis) is a condition of the body in which too many platelets, or thrombocytes, which causes excessive blood clotting.

Platelets of the blood are cell fragments that travel through the blood vessels and clot together to stop excessive bleeding, which occurs when the blood vessel is damaged. Platelets are made in the bone marrow along with red blood cells and white blood cells.

When the condition is caused by an infection or other underlying condition, it is referred to as reactive (or secondary) thrombocytosis. This is much more common than primary thrombocytosis.

What Causes Thrombocytosis?

Primary, or essential, thrombocytosis has no known cause, though it is related to an increase in platelets due to abnormal cells in the bone marrow.

Secondary Thrombocytosis may be the result of many conditions, diseases, or outside factors. It is estimated that around 35% of people with high platelet counts have some form of cancer, primarily breast cancer, lymphoma, or ovarian cancer.

Other conditions that may lead to thrombocytosis include:

Symptoms of Thrombocytosis:

Most patients with thrombocytosis do not have symptoms, but in some cases the person with Thrombocytosis may experience:

  • Bruising of the skin
  • Bleeding from the mouth, nose, gums
  • Bleeding in the intestinal tract or stomach
  • Weakness
  • Headache
  • Numbness in the hands or feet
  • Blood clots (especially while on bed rest)

How is Thrombocytosis Diagnosed?

Because symptoms are not always prevalent, thrombocytosis may not be discovered until another condition requires a thorough physical exam. Once diagnosis is confirmed via a physical exam and blood tests, a hematologist (blood disease specialist) may be recommended.

Blood tests involved in the diagnosis include:

  • Complete Blood Count, or CBC, will measure the levels of red blood cells, white blood cells, and the platelets. This test will determine how high the platelet count is.
  • Blood Smear is done via drawing a small amount of blood to be viewed via a microscope on a glass slide to determine platelet count.
  • Bone Marrow Tests will help determine if the bone marrow is healthy or not, including the production of blood cells and platelets which are made in the marrow.
    • A Bone Marrow Aspiration is performed by removing a sample of fluid bone marrow via a needle to examine the cells under a microscope.
    • A Bone Marrow Biopsy removes a sample of the marrow tissue, also via a needle, to check the types of cells in the marrow.

What are the Treatments for Thrombocytosis?

Because symptoms are not always present, treatment is not always necessary.

Regular checkups are important to monitor Thrombocytosis, and a medical professional may recommend a daily low dosage of aspirin to help prevent excessive blood clotting.

Medications that reduce the production of platelets in the bone marrow may also be used. Typically, the underlying condition is treated while watching the thrombocytosis to ensure it doesn't progress.

A procedure called plateletpheresis may be recommended for severe thrombocytosis to immediately reduce the platelet count in the blood. This procedure involves separating the platelets from the blood, similar to when donating blood, and returning the red and white blood cells to the body while leaving the platelets out.

Living With Thrombocytosis:

There are several lifestyle changes that can lower the risk of thrombocytosis flares. Stop smoking, reduce high blood pressure, reduce high cholesterol, managing your diabetes, and take all prescribed medications as recommended by your doctor.

If taking medication to lower platelet counts, make sure your doctor or dentist is aware before any major procedure, as blood thinners can increase bleeding.

Avoid over-the-counter pain medicines unless recommended by your doctor, as these can increase your risk of bleeding in the intestines.

Contact your doctor right away if you show any of the signs of internal bleeding: excessive bruising with no apparent cause, pink urine or blood in the urine, bloody stool, excessive (for you) menstrual bleeding, bleeding gums, excessive nosebleeds.

Related Resource Pages on Band Back Together:

Von Willebrand Disease


Breast Cancer


Ovarian Cancer


Blood Donation


Gestational Diabetes




Irritable Bowel Syndrome


Rheumatoid Arthritis

Celiac Disease

Deep Vein Thrombosis



Additional Resources:

Mayo Clinic offers comprehensive information about thrombocytosis as well as related conditions.

Seattle Cancer Care has information about thrombocytosis as it relates to cancer patients.