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Overview of Platelet Disorders


David J. Kuter

, MD, DPhil, Harvard Medical School

Last full review/revision Jul 2020
Topic Resources

Platelets (sometimes called thrombocytes) are cell fragments that circulate in the bloodstream and help blood to clot How Blood Clots Hemostasis is the body's way of stopping injured blood vessels from bleeding. Hemostasis includes clotting of the blood. Too little clotting can cause excessive bleeding from minor injury Too... read more . Thrombopoietin, primarily produced in the liver, stimulates the bone marrow to make large cells (megakaryocytes), which in turn make platelets from their cytoplasm. Platelets that are not used in clots circulate for 7 to 10 days and are then destroyed. About one third are always stored in the spleen.

The platelet count (number of platelets circulating in the bloodstream) is usually about 140,000 to 440,000 platelets per microliter (140 × 109 to 440 × 109 per liter). The platelet count can vary according to the menstrual cycle. It can decrease near the end of pregnancy (gestational thrombocytopenia) and increase in response to inflammation (secondary, or reactive, thrombocytosis). Neither of these conditions is serious, and most affected people have no problems resulting from either one.

Platelet disorders include

Any of these disorders can cause problems with blood clotting.

In essential thrombocythemia Essential Thrombocythemia Essential thrombocythemia is a myeloproliferative neoplasm in which excess platelets are produced, leading to abnormal blood clotting or bleeding. The hands and feet may burn, turn red, and... read more , the bone marrow cells that make platelets grow excessively and make too many platelets despite no other disorder being identified. Surprisingly, the increased number of platelets most often causes excessive bleeding rather than clotting. Doctors sometimes give people aspirin to lower the risk of abnormal clotting if they have vascular disease or are at increased risk of a heart attack. Drugs to lower the platelet count may sometimes be needed.

In thrombocytopenia Overview of Thrombocytopenia Thrombocytopenia is a low number of platelets (thrombocytes) in the blood, which increases the risk of bleeding. Thrombocytopenia occurs when the bone marrow makes too few platelets or when... read more Overview of Thrombocytopenia , there are many causes of decreased numbers of platelets. Causes are generally divided into those involving decreased production of platelets and those involving increased destruction or loss of platelets.

Symptoms of Platelet Disorders

Bleeding in the skin may be the first sign of a low platelet count or platelet dysfunction. Many tiny red dots (petechiae) often appear in the skin on the lower legs, and minor injuries (including needlesticks) may cause black-and-blue bruises (ecchymoses or purpura). The gums may bleed, and blood may appear in the stool or urine. Menstrual periods or nosebleeds may be unusually heavy. The lower the platelet count, the more severe the symptoms.

Bleeding in the Skin

Diagnosis of Platelet Disorders

  • Complete blood count

Special tests may be needed to diagnose platelet dysfunction.

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Lymphocytopenia is an abnormally low number of white blood cells in the blood. Lymphocytopenia can be acute, occurring briefly during certain conditions, or it can be chronic, occurring for a longer period of time. In addition to viral infections, which of the following is the most common cause of chronic lymphocytopenia?
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