Thrombocytopenia (Low Platelet Count) (cont.)
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Causes of thrombocytopenia can be divided into three categories:
The main causes in each category are outlined below, although there are other less common causes of low platelet count not mentioned in this article.
1. Impaired Production
Low platelet count due to impaired production is generally due to problems with the bone marrow. Usually other blood cells (red and white) are also affected by some of these processes, and their numbers may be abnormal.
Some viral infections can cause low platelet count by affecting the bone marrow, for example,
Aplastic anemia (agranulocytosis) is the terminology for bone marrow failure leading to low platelet count usually associated with anemia (low red cell count) and leukopenia or leucopenia (low white cell count). Common causes of aplastic anemia include:
Many chemotherapeutic drugs commonly cause bone marrow toxicity and thrombocytopenia.
Other causes of thrombocytopenia due to impaired bone marrow production of platelets include:
2. Increased platelet destruction
Increased platelet destruction can cause thrombocytopenia by immunologic and non-immunologic mechanisms.
Immunologic causes of thrombocytopenia can be caused by:
Idiopathic thrombocytopenic purpura (ITP) is an immunologic thrombocytopenia in which the immune system mistakenly attacks the circulating platelets (autoimmune). ITP is typically chronic (long-standing) in adults and acute in children.
Heparin-induced thrombocytopenia (HIT) is an immune destruction of platelets mediated by the use of the blood thinner heparin and its related drugs [low molecular weight heparin, called enoxaparin (Lovenox)].
Non-immunologic platelet consumptive processes include:
Severe infections or sepsis, irregular blood vessel surface (vasculitis, artificial heart valve), or, rarely, disseminated intravascular coagulation or DIC (a serious complication of overwhelming infections, traumas, burns, or pregnancy).
Other non-immunologic causes of thrombocytopenia are two other rare, but related, conditions called hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). These may result from some viral illnesses, metastatic cancers, pregnancy, or chemotherapy. Other clinical manifestations of these conditions are hemolytic anemia, kidney failure, confusion, and fever. HUS is generally associated with an infectious diarrhea in children caused by escherichia coli bacteria (E. coli O157:H7).
HELLP is an acronym for a syndrome seen in pregnant women that causes hemolytic anemia (blood cells rupture), elevated liver enzymes, and low platelets.
3. Splenic sequestration
Splenic sequestration occurs when the spleen enlarges(for example, due to cirrhosis of the liver or certain types of leukemia) and captures, or sequesters, more platelets from the circulation than normal. This could lead to thrombocytopenia.
In infants, many conditions similar to these listed above can lead to neonatal thrombocytopenia. There are also some rare genetic conditions that can also lead to thrombocytopenia in children at birth.
Pseudothrombocytopenia is term given to situations in which there is a falsely low platelet count on the blood smear reviewed by the laboratory. This can happen because of occasional clumping of the platelets together when the blood is drawn. Therefore, small number of individual platelets may be seen under the microscope, and this can be confused with true thrombocytopenia. A repeat blood draw, preferably in a tube which prevents clumping, typically solves this issue.
Dilutional thrombocytopenia is another condition that may be seen when several units of red blood cells have been transfused in a short period time. As the volume of blood expands, platelets may appear more scarce as they are distributed in a larger volume.
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