Thrombocytopenia

Definition

Thrombocytopenia is an abnormal drop in the number of blood cells involved in forming blood clots. These cells are called platelets.

Description

Thrombocytopenia is a blood disease characterized by an abnormally low number of platelets in the bloodstream. The normal amount of platelets is usually between 150,000 and 450,000 cells per microliter of blood. A microliter is an amount equal to one one-millionth of a liter (a liter is almost equal to a quart). Platelet numbers are counted by having a blood sample collected and placing a measured amount of blood in a machine called a cell counter. When the platelet number drops below 150,000 cells per microliter of blood, this person is said to be thrombocytopenic.

Causes and symptoms

Abnormal reductions in the number of platelets are caused when abnormalities occur in any of the following three processes: decreased platelet production by the bone marrow; increased trapping of platelets by the spleen; or a more rapid than normal destruction of platelets. Persons with this condition easily bruise and can have episodes of excess bleeding (a hemorrhage).

Platelets come from megakaryocytes, which are produced in the material located within the center cavity of the bones (bone marrow). When abnormalities develop in the marrow, the marrow cells can lose their ability to produce platelets in correct amounts. The result is a lower than normal level of platelets in the blood. Drugs used in cancer chemotherapy can cause the marrow to malfunction in this way, as can the presence of tumor cells in the marrow itself.

Normally, the spleen holds about one-third of the body's platelets as part of this organ's function to recycle aging or damaged red blood cells (the cells that carry oxygen in the blood). When liver disease or cancer of the spleen is present, the spleen can enlarge, resulting in a greater number of platelets staying in the organ. This condition results in abnormally low numbers of platelets in the blood.

Platelets can break down in unusually high amounts in persons with abnormalities in their blood vessel walls; with blood clots; or with man-made replacement heart valves. Devices placed inside blood vessels to keep them from closing (stents) due to weakened walls or fat build-up can also cause platelets to break down. In addition, infections and other changes in the immune system can speed up the removal of platelets from the circulation.

Diagnosis

Thrombocytopenia is diagnosed by having a blood sample taken and counting the platelets present in the sample. However, accurately determining the medical reason for this conditions is complex.

Once a low platelet count is verified, a careful evaluation of the function of the bone marrow and spleen are necessary. Improper functioning of either or both of these organs can cause thrombocytopenia. In addition, the causes for the abnormal spleen or marrow function must be investigated since different cancers, blood disorders, or liver disease can be the true cause for the drop in platelets found in the blood.

Treatment

If low platelet counts are caused by an enlarged spleen, removal of the spleen can help raise the platelet level, since the spleen is no longer there to capture the platelets. However, proper treatment for what causes the enlarged spleen is necessary as well.

Low platelet counts can indicate more serious conditions. If a dysfunctional immune system is found to be the cause for this condition, drugs like steroids or gamma globulin can be used to help maintain platelet levels in certain cases.

If low platelet levels are due to an abnormally low level of platelet production, transfusions of platelets can be given as well.

Prognosis

Thrombocytopenia can result in fatal bleeding, but it also can indicate various other, more serious, cancers and disorders that affect the blood cells. This condition requires thorough medical evaluation.

Prevention

There is no known way to prevent thrombocytopenia.

Key Terms

Gamma globulin

One of a group of proteins found in the blood that is involved in helping the body fight infections.

Stent

A man-made surgical device, usually tube-shaped, that is placed into a blood vessel to keep it from closing.

Transfusion

The transfer of blood from one person to another. Transfusions can be direct, in which blood is transferred from the donor to the recipient; or indirect, in which the blood is taken from the donor, stored in a container, and then given to the recipient.

For Your Information

Books

• Handin, Robert I. "Disorders of the Platelet and Vessel Wall." In Harrison's Principles of Internal Medicine, ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

• Sadovsky, Richard. "Management of Heparin-Induced Thrombocytopenia." American Family Physician 55 (1 May 1997): 2310.

• Winkelstein, Alan, and Joseph E. Kiss. "Immunohematologic Disorders." Journal of the American Medical Association 278 (10 Dec. 1997): 1982.

• American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.americanheart.org

Source: Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group

The Essay Author is Dominic De Bellis PhD.

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