Abstract/Text: Thrombocytopenia is a common hematologic finding with variable clinical expression. A low platelet count may be the initial manifestation of infections such as HIV and hepatitis C virus or it may reflect the activity of life-threatening disorders such as the thrombotic microangiopathies. A correct identification of the causes of thrombocytopenia is crucial for the appropriate management of these patients. In this review, we present a systematic evaluation of adults with thrombocytopenia. The approach is clearly different between outpatients, who are frequently asymptomatic and in whom we can sometimes indulge in sophisticated and relatively lengthy investigations, and the dramatic presentation of acute thrombocytopenia in the emergency department or in the intensive care unit, which requires immediate intervention and for which only a few diagnostic tests are available. A brief discussion of the most common etiologies seen in both settings is provided.

Abstract/Text: Thrombocytopenia is defined as a platelet count of less than 150 × 10(3) per µL. It is often discovered incidentally when obtaining a complete blood count during an office visit. The etiology usually is not obvious, and additional investigation is required. Patients with platelet counts greater than 50 × 10(3) per µL rarely have symptoms. A platelet count from 30 to 50 × 10(3) per µL rarely manifests as purpura. A count from 10 to 30 × 10(3) per µL may cause bleeding with minimal trauma. A platelet count less than 5 × 10(3) per µL may cause spontaneous bleeding and constitutes a hematologic emergency. Patients who present with thrombocytopenia as part of a multisystem disorder usually are ill and require urgent evaluation and treatment. These patients most likely have an acute infection, heparin-induced thrombocytopenia, liver disease, thrombotic thrombocytopenic purpura/hemolytic uremic syndrome, disseminated intravascular coagulation, or a hematologic disorder. During pregnancy, preeclampsia and the HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome are associated with thrombocytopenia. Patients with isolated thrombocytopenia commonly have drug-induced thrombocytopenia, immune thrombocytopenic purpura, pseudothrombocytopenia, or if pregnant, gestational thrombocytopenia. A history, physical examination, and laboratory studies can differentiate patients who require immediate intervention from those who can be treated in the outpatient setting. Treatment is based on the etiology and, in some cases, treating the secondary cause results in normalization of platelet counts. Consultation with a hematologist should be considered if patients require hospitalization, if there is evidence of systemic disease, or if thrombocytopenia worsens despite initial treatment.