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Thrombocytopenia

Thrombocytopenia

Description

Thrombocytopenia (thrombocythemia) is a blood disorder characterized by an abnormally low number of circulating platelets (thrombocytes) in the bloodstream. Because platelets play an important role in the process of coagulation (blood clotting) and in the plugging of damaged blood vessels, persons with decreased platelets bruise easily and can have episodes of excessive bleeding (hemorrhage). Thrombocytopenia is usually an acquired disorder, but it can also be congenital, as in neonatal rubella (German measles).

Platelets are irregular, disc-shaped fragments of large cells called megakaryocytes, which are found in the spongy center of long bones (bone marrow). They are the smallest cell-like structures in the blood. When a blood vessel is punctured or damaged, normal mature platelets have a tendency to aggregate (group) together at the site, forming a plug that stops the bleeding. The lifespan of platelets in the blood is relatively short (five to ten days), so the bone marrow of healthy individuals is continually producing new platelets to replace the old ones.

Doctors usually use a combination of the physical examination, the medical history, and laboratory testing to diagnose this disorder. The platelet count, which is part of a complete blood count (CBC), is a key diagnostic tool. It measures the number of platelets in a volume of blood. The blood normally contains between 150, 000 and 400, 000 platelets per microliter (cubic millimeter or mm3) of blood. (A million microliters is equal to one liter, or about 1.1 quarts.) In adults, a platelet count of less than 100, 000/microliter is considered low, but might occur without symptoms. Abnormal bleeding often occurs when the platelet count is below 30, 000/micro-liter. If the count falls below 10, 000/microliter, abnormal external bleeding is usually evident, and serious internal bleeding can be life threatening.

Causes

Thrombocytopenia, occurs when any of the following abnormal conditions exist:

  • decreased production of platelets by the bone marrow
  • increased destruction of circulating platelets
  • increased trapping of platelets by the spleen
  • platelet loss from hemorrhage

The most common cause of thrombocytopenia is a decrease in the production of platelets by the bone marrow. When abnormalities develop in the bone marrow, the megakaryocytes (platelet precursors) can lose their ability to produce platelets in sufficient amounts. This is a common side effect of blood cancers such as leukemia, which causes an abnormal growth of white blood cells in the bone marrow. These abnormal cells crowd out the normal bone marrow cells, including the platelets. Other diseases that cause this condition are tumors that spread (metastasize) to the bone, aplastic anemia , and viral infections such as rubella. Radiation and drugs used in cancer chemotherapy and in the treatment of other serious diseases can also cause the bone marrow to malfunction in this way, especially if they are used together. Some drugs, such as aspirin or heparin , do not actually cause a decrease in the number of platelets, but they destroy the functional ability of the platelets to aggregate.

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 (stents) placed inside blood vessels to keep them from closing (because of weakened walls or fat build-up) can also cause an increased destruction of platelets. In addition, severe microbial infections, infection with the human immunodeficiency virus (HIV), the virus that causes AIDS, and other changes in the immune system can speed up the removal of platelets from the circulation.

Normally, the spleen holds about one-third of the body's platelets as part of this organ's function to recycle certain aging or damaged blood cells. When liver disease or cancer of the spleen is present, the spleen can become enlarged (a condition called splenomegaly) and trap many more platelets than normal. Because a greater number of platelets remain in the enlarged organ, fewer platelets are circulating in the bloodstream.

Treatments

Sometimes this disorder is asymptomatic and does not require any treatment. This is often the case when thrombocytopenia occurs in children following a viral infection. Even when the disorder is a side effect of both radiation therapy and chemotherapy, if the thrombocytopenia is not severe, it is often reversible on its own once the therapies end.

Treatments, when necessary, vary with the severity of the disorder, the abnormal condition that caused the disorder, and any underlying or secondary cause. When possible, the best form of treatment is to eliminate whatever is causing the condition. For example, if a drug is causing the thrombocytopenia, eliminating that drug would be the ideal solution. However, when the disorder is a side effect of chemotherapy, the patient might need to continue the drug therapy. In such cases, the doctor must decide whether it is in the best interest of the patient to continue with the same dosage, to lower the dosage, to try an alternative drug, or to give the patient a platelet transfusion. For diseases other than blood cancers, doctors can sometimes continue the chemotherapy at full dosage by also giving the patient a platelet growth factor called Oprelvekin (marketed as Neumega) to boost the production of normal platelets in the bone marrow.

If a dysfunctional immune system is destroying the patient's platelets, the doctor might use a corticosteroid (such as prednisone) or gamma globulin to suppress the patient's immune response and to help maintain adequate platelet levels. Corticosteroids can also have unwanted side effects, so doctors usually do not use this treatment for very long.

If an enlarged spleen is the underlying cause of the thrombocytopenia, the doctor might want to try corticosteroids or epinephrine to release platelets from the spleen. If these methods fail, surgical removal of the spleen (splenectomy ) can help to raise the platelet level since the spleen is no longer there to capture the platelets. However, the disease that caused the enlarged spleen, such as lymphoma or cancer that spread to the spleen from another area of the body, should be treated as well.

If the patient is having severe external or internal bleeding as the result of injury or disease, a platelet transfusion might be necessary for immediate results. This is especially true if laboratory tests show a decreased production of platelets in the bone marrow.

Alternative and complementary therapies

A natural substance called thrombopoietin shows promise as a regulator of platelet production.

Many over-the-counter medicines, herbal supplements (such as garlic, ginger, feverfew, and ginko biloba) and vitamins can affect the ability of platelets to function properly. To determine the best treatment for a patient and to avoid drug interactions, the doctor needs to know every drug and remedy a patient is taking.

Resources

BOOKS

Altman, Roberta, and Michael J. Sarg. The Cancer Dictionary, Rev. ed. New York: Checkmark Books, 2000.

Berkow, Robert, Mark H. Beers, and Andrew J. Fletcher. The Merck Manual of Medical Information, Home ed. White-house Station, NJ: Merck Research Laboratories, 1997.

Handin, Robert I. "Disorders of the Platelet and Vessel Wall." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.

Komaroff, Anthony L. Harvard Medical School Family Health Guide. New York: Simon & Schuster, 1999.

Weinstock, Doris, Marcia Andrews, and Jane V. Cray, eds. Pro fessional Guide to Diseases, 6th ed. Springhouse, PA: Springhouse Corporation, 1998.

PERIODICALS

Henderson, C.W. "Study Results Suggest Hope for Previously Untreatable Patients." Blood Weekly (16 November 2000): 20.

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

Winkelstein, Alan, and Joseph E. Kiss. "Immunohematologic Disorders (Primer on Allergic and Immunologic Diseases)." JAMA 278 (10 December 1997): 1982.

OTHER

"Side Effect Management Series: Low Blood Platelets (Throm bocytopenia)." Oncology.com. 2001. 28 June 2001 <http://www.oncology.com>.

Beverly Miller, MT (ASCP)

Dominic De Bellis

KEY TERMS

Asymptomatic

Without symptoms.

Congenital

Existing at birth.

Gamma globulin

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

Microliter

Same as a cubic millimeter. One million microliters = 1 liter = about 1.06 quarts.

Neonatal

Relating to a newborn child.

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.

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Thrombocytopenia

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 hrombocytopenia.

Resources

ORGANIZATIONS

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

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.

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thrombocytopenia

thrombocytopenia (TCP) (throm-boh-sy-toh-pee-niă) n. a reduction in the number of platelets in the blood. This results in bleeding into the skin (see purpura), spontaneous bruising, and prolonged bleeding after injury.
thrombocytopenic adj.

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