Overview of Thrombocytopenia

ByDavid J. Kuter, MD, DPhil, Harvard Medical School
Reviewed/Revised Jun 2022 | Modified Sep 2022

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 too many platelets are destroyed or accumulate within an enlarged spleen.

  • Bleeding in the skin and bruising occur.

  • Doctors use blood tests to make the diagnosis and determine the cause.

(See also Overview of Platelet Disorders.)

Platelets are cells produced in the bone marrow that circulate in the bloodstream and help blood clot. The blood usually contains about 140,000 to 440,000 platelets per microliter (140 to 440 × 109 per liter). When the platelet count falls below about 50,000 platelets per microliter of blood (50 × 109 per liter), bleeding can occur even after relatively minor injury. The most serious risk of bleeding, however, generally does not occur until the platelet count falls below 10,000 to 20,000 platelets per microliter of blood (10 to 20 × 109 per liter). At these very low levels, bleeding may occur without any recognized injury.

Causes of Thrombocytopenia

Many disorders can cause thrombocytopenia, but these disorders fall into three main categories:

  • Too few platelets are produced

  • Too many platelets are destroyed

  • Too many platelets trapped in the spleen

Thrombocytopenia can occur when the bone marrow does not produce enough platelets, as happens in leukemia or other bone marrow disorders.

Infection with hepatitis C virus, the human immunodeficiency virus (HIV, the virus that causes acquired immunodeficiency syndrome [AIDS]), Epstein-Barr virus (the usual cause of mononucleosis), and many other viruses may result in thrombocytopenia.

Platelets can become entrapped in an enlarged spleen, as happens in cirrhosis of the liver, myelofibrosis, and Gaucher disease, reducing the number of platelets in the bloodstream.

Massive red blood cell transfusions can dilute the concentration of platelets in the blood.

Finally, the body may use or destroy too many platelets, as occurs in many disorders, three of the most notable being immune thrombocytopenia, thrombotic thrombocytopenic purpura, and hemolytic-uremic syndrome.

  • Decreased platelet production by the bone marrow (caused by bone marrow toxicity)

  • Increased platelet destruction (immune-mediated thrombocytopenia)


Symptoms of Thrombocytopenia

Bleeding in the skin may be the first sign of a low platelet count. Many tiny red dots (petechiae) often appear in the skin on the lower legs, and minor injuries may cause bruises (ecchymoses or purpura). The gums may bleed, and blood may appear in the stool or urine. Menstrual periods may be unusually heavy. Bleeding may be hard to stop.

Bleeding worsens as the number of platelets decreases. People who have very few platelets may lose large amounts of blood into their digestive tract or may develop life-threatening bleeding in their brain even though they have not been injured.

The rate at which symptoms develop can vary depending on the cause and severity of thrombocytopenia.

Bleeding in the Skin
Ecchymoses (Bruises)
Ecchymoses (Bruises)
Ecchymoses are large purple bruises seen here on the leg.


Petechiae (Skin)
Petechiae (Skin)
Petechiae are small red, purple, or brown spots as seen here in the skin.

By permission of the publisher. From Deitcher S. In Atlas of Clinical Hematology. Edited by JO Armitage. Philadelphia, Current Medicine, 2004.

Petechiae (Mouth)
Petechiae (Mouth)
Petechiae are small red spots as seen here in the mouth.


Diagnosis of Thrombocytopenia

  • Blood tests to measure platelet count and clotting

  • Other tests for disorders that may cause a low platelet count

Doctors suspect thrombocytopenia in people who have abnormal bruising and bleeding or petechiae. They often check the number of platelets routinely in people who have disorders that might cause thrombocytopenia. Sometimes they discover thrombocytopenia when blood tests are done for other reasons in people who have no bruising or bleeding.

Determining the cause of thrombocytopenia is critical to treating the condition. Certain symptoms may help determine the cause. For example, people usually have a fever when thrombocytopenia results from an infection. In contrast, they usually do not have a fever when the cause is immune thrombocytopenia, thrombotic thrombocytopenic purpura, or hemolytic-uremic syndrome.

An enlarged spleen, which a doctor may be able to feel during a physical examination, suggests that the spleen is trapping platelets and that thrombocytopenia results from a disorder that is causing the spleen to enlarge.

The platelet count may be measured with an automated counter to determine the severity of thrombocytopenia, and a sample of blood may be examined under a microscope to provide clues to its cause. A sample of bone marrow removed and examined under a microscope (bone marrow biopsy and aspiration) may occasionally be needed to provide information about platelet production.

Treatment of Thrombocytopenia

  • Treatment of cause of thrombocytopenia

  • Avoidance of injury to minimize risk of bleeding

  • Drugs that increase production or decrease destruction of platelets

  • Sometimes platelet transfusion

Treating the cause can often treat the thrombocytopenia. Thrombocytopenia caused by a drug usually is corrected by stopping the drug. Thrombocytopenia caused by autoimmune destruction of platelets (as in immune thrombocytopenia

People who have a very low platelet count are often treated in a hospital. When bleeding is severe, platelets may be transfused, although sometimes the transfused platelets also are destroyed by the underlying disorder.

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