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Overview of Thrombocytopenia


David J. Kuter

, MD, DPhil, Harvard Medical School

Last full review/revision Jul 2020
Topic Resources

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.

  • Sometimes treatment (such as platelet transfusion, prednisone and drugs to increase platelet production, or removal of the spleen) is needed.

Platelets are cells that circulate in the bloodstream and help blood 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 . The blood usually contains about 140,000 to 440,000 platelets per microliter (140 × 109 to 440 × 109 per liter). When the platelet count falls below about 50,000 platelets per microliter of blood (50 × 10 9 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 × 109 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.

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

Some drugs such as heparin, certain antibiotics, ethanol, anticancer drugs, and quinine can also cause thrombocytopenia. Drug-induced cytopenia may be the result of

  • 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

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. 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 Bone Marrow Examination Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Sometimes a sample of bone marrow must be examined to determine... read more ) may occasionally be needed to provide information about platelet production.

Treatment of Thrombocytopenia

  • Treatment of cause of thrombocytopenia

  • Avoidance of injury and drugs that affect 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 Immune Thrombocytopenia (ITP) Immune thrombocytopenia (ITP) is a bleeding disorder caused by decrease in the number of platelets (thrombocytes) that occurs in a person who does not have another disorder that affects platelets... read more Immune Thrombocytopenia (ITP) ) is treated with prednisone to lessen platelet destruction, drugs to increase production of platelets in the bone marrow, and sometimes removal of the spleen (splenectomy).

People with a low platelet count and abnormal bleeding usually should not take drugs that impair platelet function (such as aspirin or nonsteroidal anti-inflammatory drugs).

People who have a very low platelet count are often treated in a hospital. When bleeding is severe, platelets may be transfused Overview of Blood Transfusion A blood transfusion is the transfer of blood or a blood component from one healthy person (a donor) to a sick person (a recipient). Transfusions are given to increase the blood's ability... read more Overview of Blood Transfusion , although sometimes the transfused platelets also are destroyed by the underlying disorder.

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