The Function of Blood Platelets or Thrombocytes

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Platelets, also known as thrombocytes, are blood cells responsible for blood clotting. If a blood vessel wall becomes damaged, platelets will rush to the site of injury and form a plug or clot to stop the bleeding. If platelet count is low (a condition called thrombocytopenia), the risk of uncontrolled or prolonged bleeding increases. When there are too many platelets in the blood (a condition called thrombocytosis), it may lead to abnormal blood clot formation, which can be serious and life-threatening.

Your healthcare provider can help you assess your platelet count by looking at a complete blood count (CBC) test.

The root thrombo in thrombocyte means clot. You'll see it used with diseases and conditions that affect platelets and blood clotting.

Close up of scientists hands selecting a blood sample for medical testing
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What Platelets Do

Platelets are one of three types of blood cells (in addition to red blood cells and white blood cells) that originate in the bone marrow from cells known as megakaryocytes.

The process by which platelets form a clot is called adhesion. For example, if you accidentally cut your finger and rupture a blood vessel, it will start to bleed. In order to stop the bleeding, platelets within that broken vessel adhere to the site of injury and send out chemical signals for more help.

More platelets answer the call and begin to connect to each other to form a plug in a process called aggregation . Once a plug or clot is formed in the blood vessel wall, the clotting (coagulation) cascade is activated, which then adds fibrin (a structural protein) to the clot to knit it together. Fibrin is responsible for the scab you may see at a cut site.

Aspirin and some non-steroidal anti-inflammatory drugs inhibit normal platelet function, which is why you may be asked to stop using them for a period of time before a surgery or procedure.

Testing and Your Platelets

An overview of the numbers, size, and health of platelets is included in a complete blood count (CBC) test, a standard lab panel of bloodwork that analyzes the makeup and chemistry of blood.

The specific lab markers that refer to platelets are as follows:

Platelet Count (PLT)

Just as it sounds, this is the actual number of platelets you have (per microliter of blood).

  • Low range: Less than 150,000 platelets per microliter
  • Normal range: 150,000 to 450,000 platelets per microliter
  • Elevated range: 500,000 to 1,000,000 platelets per microliter

If your platelet count falls below 50,000, you may experience prolonged bleeding times.

Platelet count is an important number for your healthcare provider to know before and after surgery to predict any potential bleeding and clotting problems. It is also an important marker during chemotherapy and radiation therapy, as these treatments may inhibit the production of platelets in the bone marrow.

Mean Platelet Volume (MPV)

The mean platelet volume (MPV) is the average size of the platelets. Younger platelets are larger than older ones, so an elevated number means you are producing and releasing them rapidly, while a low number means altered production in the bone marrow.

Platelets are live in the bloodstream for about eight to 10 days.

Platelet Distribution Width (PDW)

PDW is the variation in the size of the platelets, which can indicate conditions that affect the platelets.

Platelet function tests may also be performed if there are symptoms of or potential for excessive bleeding, and to also monitor anti-platelet medications.

Causes of Low Platelet Count

If the body doesn't have enough platelets in circulation, you may develop a condition called thrombocytopenia.

The following factors may contribute to low platelet count:

  • Chemotherapy or radiation therapy: These treatments suppress or kill off the blood-producing cells (megakaryocytes) in your bone marrow, leading to low platelet production.
  • Viral infections: Hepatitis C or HIV infections may attack bone marrow, affecting thrombocyte production.
  • Autoimmune conditions, such as lupus or immune thrombocytopenic purpura
  • Pregnancy: Hemolysis, elevated liver enzymes, low platelet count syndrome, better known as HELLP, in pregnancy is a variant of pre-eclampsia and may result in the breakdown of blood cells and platelets.
  • Medications: Anticoagulants such as warfarin and heparin may inhibit platelet production.

Other examples of conditions that may cause thrombocytopenia include having a mechanical heart valve, heparin antibodies, chronic alcohol abuse, liver disease, severe sepsis, and toxic exposures.​

A platelet count below 20,000 per microliter is a life-threatening risk as spontaneous bleeding may occur and be hard to stop. At that level, you may be given a platelet transfusion.

Causes of High Platelet Count

If the body has too many platelets in circulation, you may develop a condition called thrombocytosis.

The following factors may contribute to high platelet count:

  • Primary bone marrow disorder: Essential thrombocytosis is a condition in which the megakaryocytes in bone marrow produce too many platelets, increasing the risk of blood clots.
  • Chronic inflammation in the body: Inflammatory conditions such as rheumatoid arthritis (RA) and inflammatory bowel disease (IBD) may result in elevated platelet counts as high levels of inflammation may cause the bone marrow to produce more white blood cells and platelets to combat cellular damage.
  • Infection: Bone marrow cells increase production of white blood cells and platelets to help fight infection, causing an elevation in platelet count.
  • Iron deficiency anemia: Reactive or secondary thrombocytosis may result when the body is undergoing a breakdown of red blood cells and the bone marrow cells go into overproduction to meet needs.
  • Spleen removal: Up to one-third of platelets are stored in the spleen at any time, and so removal of this organ will cause an increase in platelet concentration in the bloodstream. This is generally a temporary condition, however.
  • Cancer: High platelet counts can also be seen in cancer, especially with gastrointestinal cancer, as well as lymphoma, lung, ovarian, and breast cancer. This is thought to be due to the inflammation associated with the malignancy stimulating the production of platelets in the bone marrow.

In addition, a temporary increase in the platelet count can happen after major surgery or trauma.

A Word From Verywell

Platelets are tiny cells with a highly important function in the body—to stop bleeding. There is a wide range of normal in terms of platelet count, but it's important to be aware of the extremes, too, especially if you're considering surgery or undergoing another procedure that may require bleeding and clotting. If you have very low or very high levels of platelets, make sure you're communicating with your healthcare provider about a safe plan of action.

Frequently Asked Questions

  • How are low blood platelets treated?

    Treatment is only necessary if thrombocytopenia is causing health problems. Treatment may include blood transfusion, which is a temporary fix; spleen removal; and medications that may include steroids and immunoglobulins.

  • How are high blood platelets treated?

    Many people who experience high blood platelets, or thombocytosis, do not require treatment but may be monitored regularly by their healthcare provider. If symptoms are problematic, treatment may include daily low-dose aspirin to prevent blood clots, medications that reduce platelet production, and treating the underlying cause of the condition.

  • What do blood platelets look like?

    Under a microscope, blood platelets look like small plates when inactive. When activated, they look like an octopus as they grow small tentacles.

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6 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. University of Rochester Medical Center. Health Encyclopedia. What Are Platelets?

  2. Merck Manual Professional Version. Thrombocytopenia: Other Causes. Revised February 2019.

  3. Natioinal Heart, Lung, and Blood Institute. Thrombocythemia and Thrombocytosis.

  4. Cleveland Clinic. Thombocytopenia. Updated November 23, 2020.

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

  6. Johns Hopkins Medicine. What are platelets and why are they important?

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