ThrombocytopeniaThrombocytopenia is defined as a decreased number of platelets in the blood.
Blood platelets, or thrombocytes, are not true cells, but rather cytoplasmic fragments of a large cell in the bone marrow, the megakaryocyte, and these fragments in the blood help with clotting.
Platelets become activated when there is injury to the blood vessel wall causing the platelets in the vicinity to adhere to the damaged area and become cohesive to other platelets. This aggregation leads to the formation of a platelet plug (clot), which prevents further blood loss and allows the blood vessel repair process to begin. However, if the platelet count is low, then the blood does not clot normally. This is due to failure of the platelets to seal over microscopic breaches in blood vessel walls.
Usually, the platelet count is about 150,000 to 350,000 platelets in a microliter of blood. However, in people with a low platelet count, bleeding is more likely to occur, even after a slight injury; and when the platelet count is very low (below 20,000), massive, life threatening bleeding may occur even when there is no injury.
Decreased Production
Leukemia, lymphomas, infection with human immunodeficiency virus (HIV, which causes AIDS), drinking alcohol, and a variety of other bone marrow disorders can cause the bone marrow to produce an insufficient number of platelets.
In addition, platelets can become trapped and fewer platelets remain in the bloodstream causing the platelet count to decrease if the spleen enlarges due to the liver becoming cirrhotic, or when a form of leukemia affecting the bone marrow called myelofibrosis develops gradually changing the bone marrow tissue into scar tissue and inhibiting the bone marrow’s ability to create new blood cells.
Increased Destruction
The body may use or destroy too many platelets. HIV infection, lupus (systemic lupus erythematosus), idiopathic thrombocytopenic purpura, thrombotic thrombocytopenic purpura, and hemolytic-uremic syndrome can have this effect. Some drugs, such as heparin and certain antibiotics, also have this effect.
If the immune system produces abnormal antibodies that destroy the body's platelets the bone marrow produces more platelets to compensate but cannot keep up with the demand and a condition know as idiopathic thrombocytopenic purpura develops.
Taking heparin may cause a low platelet count. Heparin is a drug that makes blood less likely to clot (anticoagulant). But paradoxically, it sometimes stimulates clot formation. Then the platelet count decreases because so many platelets are used up.
Platelet Dysfunction
Aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and antihistamines may interfere with how platelets function, although the platelet count remains normal, and this is NOT a thrombocytopenia.
Symptoms
Bleeding in the skin may be the first sign that the platelet count is low. Often, many tiny red dots appear in the skin on the lower legs. People may bruise easily. Slight injuries sometimes cause small scattered bruises. The gums may bleed, and blood may appear in the stool or urine. Bleeding due to injuries may be hard to stop.
Bleeding worsens as the platelet count decreases. When the count is below 20,000, bleeding in the digestive tract or brain may occur even when there is no injury. |
