This topic review will provide an overview describing the most common medical disorders to be found in adults with newly recognized thrombocytopenia, who may present in a primary care setting. It will also provide a general guideline for outpatient management of the thrombocytopenic patient as concerns activity restrictions, safety of invasive procedures, and use of antiplatelet and anticoagulant agents.
General approaches to thrombocytopenia in adults and to the patient presenting with a bleeding diathesis are presented separately. (See "Approach to the adult patient with thrombocytopenia" and "Approach to the adult patient with a bleeding diathesis".)
WHAT IS A LOW PLATELET COUNT?
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. (See 'Follow-up of minimal asymptomatic thrombocytopenia' below and "Approach to the adult patient with thrombocytopenia", section on 'Definitions and normal values'.)
ISOLATED ASYMPTOMATIC THROMBOCYTOPENIA
The most common office or outpatient presentation of a patient with isolated thrombocytopenia is the unexpected discovery of a low platelet count during a routine evaluation (table 1). The diagnostic evaluation of these patients, as described below, guides their appropriate management.
Laboratory error — A number of errors may contribute to a falsely low platelet count: