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.
Generally speaking a normal platelet count ranges from 150,000 and 450,000 per mm3. These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessarily imply any form of disease. The number of platelets in a blood sample also decreases rather quickly with time and a low platelet count may be caused by a delay between sampling and analysis. Thrombocytopenia is any disorder in which there are not enough platelets. Platelets are cells in the blood that help blood to clot. This condition is sometimes associated with abnormal bleeding.
The acquired form is more common, especially among elderly. In either case, it usually results from decreased or defective production of platelets in the bone marrow (for example, in leukemia, aplastic anemia and with toxicity from certain drugs), increased destruction outside the marrow caused by an underlying disorder (such as cirrhosis of the liver, disseminated intravascular coagulation and severe infection) or dilution of platelets.
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 the human immunodeficiency virus (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.
Bleeding from the nose and the gums is also quite common. More serious haemorrhage can occur at the back of the eye (retina), sometimes threatening sight.The most serious complication, which is potentially fatal, is spontaneous bleeding inside the head (intracranial) or from the lining of the gut (gastrointestinal).
Acute ITP in children often goes away on its own within a few weeks or months and doesn’t return. In 80 percent of children who have ITP, the platelet count returns to normal within 6 to 12 months. Treatment may not be needed. A small number of children, about 5 percent, whose ITP doesn’t go away on its own may need to have further medical or surgical treatment.
Thrombocytopenia may be caused by infections in the fetus or newborn such as rubella, syphilis, and bacterial or viral infections. It can also develop when a mother's immune system produces antibodies against the baby's platelets. Some medications taken by the mother or given to the baby can cause thrombocytopenia.
Platelets can breakdown 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 breakdown. In addition, infections and other changes in the immune system canspeed up the removal of platelets from the circulation.
