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Thrombocytopenia is defined as a below normal number of platelets in the circulating blood. It is the most common cause of abnormal bleeding. The pathophysiology of thrombocytopenia is similar to that of anemia, but the latter is better understood. Thus, despite the number and diversity of disorders that may be associated etiologically, thrombocytopenia results from only four processes: artifactual thrombocytopenia, deficient platelet production, accelerated platelet destruction, and abnormal distribution or pooling of the platelets within the body thrombocytopenia and low platelets.
Artifactual thrombocytopenia, or falsely low platelet counts, occurs ex vivo, when platelets are not counted accurately. This mechanism should be considered in patients who have thrombocytopenia but no petechiae or ecchymoses. Although inaccurate counting may occur in the presence of thrombocytopenia.
Accelerated platelet destruction is the most common cause of thrombocytopenia. It leads to stimulation of thrombopoiesis and consequently to an increase in the number, size, andrate of maturation of the precursor megakaryocytes. When the rate of platelet destruction exceeds this compensatory increase in platelet production, thrombocytopenia develops.
Deficient platelet production may result from any of a number of processes. Those that depopulate the stem cell or megakaryocyte compartments are the most common, such as marrow injury by myelosuppressive drugs or irradiation and aplastic anemia. Deficient platelet production also may be the cause.
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