What are platelets?


Platelets are tiny cell fragments in the blood that help stop bleeding. They are also called thrombocytes. Unlike red and white blood cells, platelets are not complete cells. Instead, they are small pieces of larger bone marrow cells called megakaryocytes. Under the microscope, platelets look much smaller than red or white blood cells and often appear as small purple dots on a blood smear.

What do platelets do?

The main job of platelets is to help the blood clot after an injury. When a blood vessel is damaged, platelets quickly move to the area, stick to the broken surface, and clump together. They release chemicals that attract more platelets and activate proteins in the blood known as clotting factors. Together, this process forms a blood clot that stops bleeding and allows the vessel to begin healing.

Where are platelets found?

Platelets are made in the bone marrow by megakaryocytes. After being released into the bloodstream, they circulate throughout the body and are always ready to respond if a blood vessel is injured. Platelets normally live for about 7 to 10 days before being removed from the blood by the spleen.

Common medical conditions associated with changes in platelets

The number and function of platelets are important for health. Abnormalities can increase the risk of bleeding or clotting.

Common conditions include:

  • Thrombocytopenia: A low platelet count. This can happen after chemotherapy, with certain medications, from autoimmune diseases, infections, or bone marrow disorders. People with thrombocytopenia may bruise easily or bleed longer than normal after an injury.

  • Thrombocytosis: A high platelet count. This may be a temporary reaction to inflammation, infection, or blood loss, or it may be caused by bone marrow diseases such as essential thrombocythemia. Too many platelets can increase the risk of abnormal blood clots.

  • Platelet function disorders: In some conditions, platelet numbers are normal but they do not work properly. This can be inherited (genetic) or acquired, for example from medications like aspirin.

  • Bone marrow diseases: Conditions such as leukemia, aplastic anemia, or myelodysplastic syndrome can reduce the number or change the appearance of platelets.

Questions to ask your doctor

  • What did my platelet count show?

  • Is my platelet count too low, too high, or normal?

  • Do my platelets look normal under the microscope?

  • Could my platelet changes be caused by a medication, infection, or bone marrow disease?

  • Do I need further tests, such as a bone marrow biopsy or special platelet function studies?

  • How will these results affect my treatment or follow-up care?

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