Two blood samples that will be tested for Thrombocytosis.

How to Test for Thrombocytosis: High Platelet Count

Two blood samples that will be tested for Thrombocytosis.

Thrombocytosis occurs when bone marrow manufactures an excessive amount of blood platelets. Platelets help support the clotting of blood, which stops bleeding. However, when platelet levels are too high, it can cause dangerous side effects like stroke or heart attack. If you display symptoms or believe you are at risk, it is vital to seek thrombocytosis testing to help determine the cause and seek the proper treatment. 

This article will share more about thrombocytosis and how to test for it.

What is Thrombocytosis?

If your doctor determines that you have thrombocytosis, then this means that you have too high of a platelet count. Platelets are special blood cells that help the blood clot, allowing the blood cells to bond together to stop bleeding. Platelets are essential, but abnormally high levels are unsuitable for the long-term health of your body.

Testing for thrombocytosis begins with a simple blood draw. A couple of blood tests help to check for and evaluate thrombocytosis, including a complete blood count and an MPV blood test.

High Platelet Count Symptoms

Thrombocytosis often does not cause any symptoms. When symptoms do occur, it is usually a result of the underlying condition causing the high platelet count or abnormal clotting or bleeding in the body.

Symptoms in Children

Thrombocytosis in children is usually related to an underlying infection, inflammation, or iron-deficiency anemia. High platelet counts in children are considered a type of pediatric platelet disorder and may cause symptoms such as small or large bruises on the skin.

Symptoms in Adults

Common symptoms of thrombocytosis in adults include:

  • Headache
  • Confusion
  • Changes in speech
  • Chest pain
  • Shortness of breath
  • Weakness
  • Burning on the hands or feet
  • Abnormal bleeding such as nose bleeds, bruises, blood in the stool, or bleeding gums.

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High Platelet Count Causes

Test Tubes in Close Up Shot that are tested for High Platelet Count. There are different types of thrombocytosis, and they have other causes. The two main types of thrombocytosis include primary thrombocytosis and secondary thrombocytosis.

Primary High Platelet Count

You may also hear primary thrombocytosis referred to as essential thrombocythemia. This thrombocytosis type occurs when the body produces too many platelets within the bone marrow. When the blood cell production in the bone marrow is abnormal, you can have too many platelets.

Secondary High Platelet Count

Secondary thrombocytosis occurs when an external cause triggers an abnormal platelet count. This type of thrombocytosis could result from a medical condition, an injury, an infection, surgery, or medication.

Certain medications can trigger a rare secondary thrombocytosis type, sometimes called medication-induced thrombocytosis.1 Some medications that might cause thrombocytosis include low-molecular-weight heparins, retinoic acid, certain antibiotics, clozapine, epinephrine, and gemcitabine.

Diagnostic Tests for Thrombocytosis

Because thrombocytosis does not typically cause symptoms until it has gotten more severe, it is typically first detected on routine blood work. Standard diagnostic tests for thrombocytosis include complete blood count (CBC), bone marrow aspiration and biopsy, genetic testing, and imaging tests.

Complete Blood Count (CBC) 

A complete blood count or CBC is a blood test used to evaluate health by looking at several different values, including:

  • Red blood cells
  • White blood cells
  • Hemoglobin
  • Hematocrit
  • Platelets

CBCs are often part of routine blood work.

MPV Blood Test

An MPV blood test may help evaluate the size of your platelets. MPV stands for mean, platelet, and volume. By measuring the average platelet size in a blood sample, this test can give your healthcare provider an idea of how healthy or normal your platelets are.

Bone Marrow Aspiration and Biopsy

If your doctor finds that you have abnormal platelet levels, they may order a bone marrow aspiration and biopsy to help detect any abnormalities in blood cell formation. This procedure involves collecting and sending a bone marrow sample to a lab for testing. Bone marrow is the porous tissue inside the bones, where blood cells form.

Genetic Testing

Genetic testing pinpoints whether genetics are the cause of thrombocytosis. Gene mutations are prevalent in primary thrombocytosis.

Thrombocytosis Treatment

Female doctor consulting a female patient about her thrombocytosis blood test results. If your thrombocytosis is not causing symptoms, it may only require regular checkups to monitor your levels. However, your doctor may recommend specific treatment options for thrombocytosis, including medication and plateletpheresis.

  • Medication Therapy: Certain medications like hydroxyurea and anagrelide can help lower platelet counts.
  • Plateletpheresis: A procedure that can filter out extra platelets from the blood, usually only used when platelet levels are so high that you are at risk of life-threatening blood clots.


Thrombocytosis occurs when platelet levels are higher than they should be. High platelet counts can put you at risk of a blood clot when left untreated. Being knowledgeable about and staying abreast of your platelet levels is critical so that you can find a treatment option if your levels are abnormal. Platelet counts become elevated for a variety of reasons. Consulting with a medical professional can help determine if you are at risk of thrombocytosis and require testing.

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Lab Testing - Frequently Asked Questions

Why is it important to do lab tests occasionally?

It is important to do lab tests occasionally because they can provide valuable information about an individual's health and help to identify potential health issues early on. Lab tests can measure a wide range of factors, including blood count, cholesterol levels, liver and kidney function, and hormone levels, and can provide insight into an individual's overall health and wellness. Additionally, lab tests can help to diagnose and monitor the progression of certain medical conditions, such as diabetes and heart disease, and can help to identify any potential health risks or concerns. By doing lab tests occasionally, individuals can take proactive steps to maintain their health and wellbeing and reduce the risk of potential health problems in the future.

What does a routine blood test cover?

A routine blood test is used to check for a range of things, including your blood count and the levels of certain chemicals and substances in your blood. Blood tests can also be used to check how well certain organs, such as your liver and kidneys, are functioning.

How is a blood sample collected for lab testing?

A blood sample for lab testing is typically collected through a process called venipuncture, which involves inserting a small needle into a vein to draw blood. This is usually done on the inside of the elbow or the back of the hand.

What is the cost of a lab test?

In general, the cost of a lab test can range from a few dollars to several hundred dollars. It is always best to consult with your doctor or healthcare provider to get an accurate estimate of the cost of a lab test.

Read More: Lab Testing FAQ