Thrombocytopenia (low platelet level) can result from variousfactors: decreased production of platelets within the bone marrow, increased destruction of platelets, or increased consumption of platelets. Causes and treatments are summarized in Table 33-5.
Bleeding and petechiae usually do not occur with platelet counts greater than 50,000/mm3, although excessive bleeding can follow surgery or other trauma. When the platelet count drops below 20,000/mm3, petechiae can appear, along with nose and gingival bleeding, excessive menstrual bleeding, and excessive bleeding after surgery or dental extractions.
When the platelet count is less than 5000/mm3, spontaneous, potentially fatal central nervous system or gastrointestinal hemorrhage can occur. If the platelets are dys-functional due to disease (eg, MDS) or medications (eg, aspirin), the risk of bleeding may be much greater even when the actual platelet count is not significantly reduced.
A platelet deficiency that results from decreased production (eg, leukemia, MDS) can usually be diagnosed by examining the bone marrow via aspiration and biopsy. When platelet destruction is the cause of thrombocytopenia, the marrow shows increased mega-karyocytes (the cells from which the platelets originate) and nor-mal or even increased platelet production as the body attempts to compensate for the decreased platelets in circulation. Another cause of thrombocytopenia is sequestration. Approximately one third of the circulating platelets are within the spleen, and a greatly enlarged spleen results in increased sequestration of platelets.
The management for secondary thrombocytopenia is usually treatment of the underlying disease. If platelet production is im-paired, platelet transfusions may raise the platelet count and stop bleeding or prevent spontaneous hemorrhage. If excessive platelet destruction occurs, transfused platelets will also be destroyed, and the platelet count will not rise. The most common cause of ex-cessive platelet destruction is ITP (see the following discussion). In some instances splenectomy can be a useful therapeutic inter-vention, but often it is not a therapeutic option, for example in patients in whom the enlarged spleen is due to portal hyperten-sion related to excessive alcohol consumption.
The interventions for a patient with thrombocytopenia are de-lineated in Chart 33-10.