The clinician is frequently faced by a patient presenting with a low platelet count, the cause of which is not immediately apparent. This topic will provide a structure through which the cause(s) of such thrombocytopenia can be assessed. A related topic describes the most common outpatient and inpatient presentations of adults with newly recognized isolated thrombocytopenia (ie, patients in whom the remainder of the blood count is normal, and who may or may not have signs of systemic disease) and provides a general guideline for the evaluation and management of thrombocytopenic patients in the office and hospital settings. (See "Evaluation and management of thrombocytopenia by primary care physicians".)
Other issues related to thrombocytopenia are presented separately:
●Thrombocytopenia in pregnancy. (See "Thrombocytopenia in pregnancy".)
●Evaluation of the patient with a bleeding diathesis. (See "Approach to the adult patient with a bleeding diathesis".)
DEFINITIONS AND NORMAL VALUES
The normal platelet count in adults ranges from 150,000 to 450,000/microL, with mean values of 237,000 and 266,000/microL in males and females, respectively . Thrombocytopenia is defined as a platelet count less than 150,000/microL (150 x 109/L), keeping in mind that 2.5 percent of the normal population will have a platelet count lower than this.