Hematologic Conditions: Platelet Disorders.

Platelets have an important role in hemostasis. Platelet disorders occur when too few or too many platelets are present, or when platelet functions are abnormal. Thrombocytopenia, defined as a platelet count less than 150,000/mcL, can be acute or chronic and congenital or acquired. Severe thrombocytopenia is associated with life-threatening bleeding and thrombotic complications. A comprehensive history and physical examination are central to the diagnostic approach. These elements should focus on identification of concurrent conditions associated with thrombocytopenia and differentiation among three mechanisms: decreased platelet production, increased platelet consumption, and platelet sequestration. Although previously thought to be the result of a single process, thrombocytopenia often is due to a combination of factors. Thrombocytosis is present when the platelet count is elevated. The principal types are essential (primary) thrombocythemia and reactive (secondary) thrombocytosis. Essential thrombocythemia is a myeloproliferative neoplasm associated with mutations of genes that regulate thrombopoiesis (eg, JAK2). It can lead to thrombotic and hemorrhagic complications. Reactive thrombocytosis frequently is encountered in the family medicine setting. It rarely causes vascular complications or requires management beyond that required for the underlying condition. Written permission from the American Academy of Family Physicians is required for reproduction of this material in whole or in part in any form or medium.