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Overview of Thrombocytopenia

By

David J. Kuter

, MD, DPhil, Harvard Medical School

Last full review/revision Jul 2020| Content last modified Jul 2020
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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. 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

Many disorders can cause thrombocytopenia.

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.

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)

Table
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Causes of Thrombocytopenia

Mechanism

Examples

Bone marrow does not produce enough platelets

Heavy alcohol consumption

Vitamin deficiency anemias, including vitamin B12 and folate deficiency anemias

Some bone marrow disorders

Some chemotherapy drugs

Platelets become entrapped in an enlarged spleen

Cirrhosis of the liver that causes spleen enlargement due to abnormally high blood pressure in the large vein that brings blood from the intestine to the liver

Platelets become diluted

Massive red blood cell replacement or exchange transfusion; stored red blood cells do not contain very many platelets

Use or destruction of platelets increases

Drugs such as heparin, quinine, many antibiotics (such as trimethoprim/sulfamethoxazole, rifampin, and vancomycin), and some oral drugs for diabetes

Conditions involving disseminated intravascular coagulation within blood vessels, as can occur with complications of childbirth, cancer, blood poisoning (septicemia) due to gram-negative bacteria, and traumatic brain damage

Symptoms

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

  • 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) may occasionally be needed to provide information about platelet production.

Treatment

  • 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) 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, although sometimes the transfused platelets also are destroyed by the underlying disorder.

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