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Chapter 173. Bleeding and Clotting Disorders
Topics: Introduction | Hereditary Hemorrhagic Telangiectasia | Allergic Purpura | Thrombocytopenia | Von Willebrand's Disease | Hemophilia | Thrombophilia | Disseminated Intravascular Coagulation
 
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Thrombocytopenia

Thrombocytopenia is a deficiency of platelets (thrombocytes).

The blood usually contains about 150,000 to 350,000 platelets per microliter. Bleeding can occur with relatively minor trauma when the platelet count falls below 20,000 to 30,000 platelets per microliter of blood. The most serious risk of bleeding, however, generally does not occur until the platelet count falls below 10,000 platelets per microliter. At these very low levels, bleeding may occur without any injury.

Causes

Many diseases can cause thrombocytopenia. Thrombocytopenia can occur when the bone marrow does not produce enough platelets, as happens in leukemia and some anemias. Infection with HIV, the virus that causes AIDS, often results in thrombocytopenia. Platelets can become entrapped in an enlarged spleen, as happens in myelofibrosis and Gaucher's disease, reducing the number of platelets in the bloodstream. Massive blood 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 idiopathic thrombocytopenic purpura, thrombotic thrombocytopenic purpura, and hemolytic-uremic syndrome.

click here to view the sidebar See the sidebar Causes of Thrombocytopenia.

Idiopathic thrombocytopenic purpura is a disease in which antibodies form and destroy the body's platelets. Why the antibodies form is not known. Although the bone marrow increases platelet production to compensate for the destruction, the supply cannot keep up with the demand.

Thrombotic thrombocytopenic purpura is a rare disease in which small blood clots form suddenly throughout the body. The blood clots mean that an abnormally high number of platelets are being used, which leads to a sharp decrease in the number of platelets in the bloodstream.

Hemolytic-uremic syndrome is a disorder in which the number of platelets suddenly decreases, red blood cells are destroyed, and the kidneys stop functioning. Hemolytic-uremic syndrome is rare but can occur with certain bacterial infections and with the use of certain chemotherapy drugs, including mitomycin. It is most common in infants, small children, and women who are pregnant or have just given birth, although it can occur in older children, adults, and women who are not pregnant.

Symptoms and Complications

Bleeding in the skin may be the first sign of a low platelet count. Many tiny red dots often appear in the skin on the lower legs, and minor injuries may cause small scattered bruises. 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 the digestive tract or may develop life-threatening bleeding in the brain even though they have not been injured.

The rate at which symptoms develop can vary depending on the cause of thrombocytopenia. For example, in thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome, symptoms develop suddenly. In idiopathic thrombocytopenic purpura, symptoms may develop suddenly or gradually and subtly.

Symptoms in thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome are quite distinct. In thrombotic thrombocytopenic purpura, the small blood clots that develop (using up platelets) cause a wide range of symptoms and complications, some of which can be life threatening. Symptoms that result from clots in the brain may include headache, confusion, seizures, and coma. Symptoms that result from clots elsewhere in the body include abnormal heart rhythms, blood in the urine that accompanies kidney damage, and abdominal pain. The predominant symptoms and complications of hemolytic-uremic syndrome are related to kidney damage, which is usually severe and may progress to kidney failure.

Diagnosis

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 cause thrombocytopenia. Sometimes they discover thrombocytopenia when blood tests are performed 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 idiopathic 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 causes the spleen to enlarge. Hemolytic-uremic syndrome is diagnosed when poor kidney function is identified by blood tests that show high levels of urea nitrogen and creatinine.

A sample of blood may be examined under a microscope, or the platelet count may be measured with an electronic counter to determine the severity of thrombocytopenia and provide clues to its cause. A sample of bone marrow removed and examined under a microscope (bone marrow aspiration and biopsy (see Section 14, Chapter 170)) may be needed to provide information about platelet production.

Treatment

People who have a very low platelet count are often treated in a hospital or advised to stay in bed to avoid accidental injury. When bleeding is severe, platelets may be transfused.

Addressing the underlying cause can often treat the thrombocytopenia. Thrombocytopenia caused by a drug usually is corrected by discontinuing the drug. The effects produced by antibodies that destroy platelets in idiopathic thrombocytopenic purpura can be blocked temporarily with a corticosteroid (for example, prednisone), allowing the number of platelets to increase. Danazol may have similar effects as prednisone. Drugs that suppress the immune system, including cyclophosphamide and sometimes azathioprine, may reduce the formation of antibodies. Most people with idiopathic thrombocytopenic purpura eventually require surgical removal of the spleen (splenectomy) to increase the number of platelets. People with thrombotic thrombocytopenic purpura are often treated with plasma transfusions along with plasmapheresis (see Section 14, Chapter 171). The two procedures together are called plasma exchange.

Complications that require long-term treatment can result from some causes of thrombocytopenia. For example, the number of platelets usually increases as people recover from the hemolytic-uremic syndrome; however, lifelong dialysis or kidney transplantation may be needed if the kidney failure persists.

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