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Thrombocytopenia and disorders of platelet function 

Thrombocytopenia and disorders of platelet function
Chapter:
Thrombocytopenia and disorders of platelet function
Author(s):

Nicola Curry

, and Susie Shapiro

DOI:
10.1093/med/9780198746690.003.0545
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date: 28 July 2021

The platelet is the smallest circulating blood cell. In health, it plays a vital role in haemostasis, and in disease contributes to problems of bleeding and/or thrombosis. The number of platelets produced is under tight homeostatic control, regulated by the cytokine thrombopoietin. A normal platelet count lies within the range 150 to 450 × 109/litre. Thrombocytopenia is defined as a reduction in the number of circulating platelets to fewer than the normal reference range (typically <150 × 109/litre). Spontaneous bleeding is uncommon unless the platelet count falls below 10 to 20 × 109/litre or unless there is abnormal platelet function. Thrombocytopenia can be classified according to three main pathologies: (1) increased platelet destruction, (2) reduced platelet production, and (3) increased platelet sequestration. Disorders of increased platelet destruction may be immune mediated or nonimmune. Primary immune thrombocytopenia (ITP) is an acquired disorder affecting both adults and children, characterized by an isolated thrombocytopenia (platelet count <100 × 109 /litre) for which no precipitant can be found. Primary ITP is a diagnosis of exclusion. Corticosteroids are the main first-line therapy for adult ITP, commonly prednisolone. Nonimmune causes of platelet destruction include microangiopathic haemolytic disorders such as thrombotic thrombocytopenic purpura, haemolytic uraemic syndrome, and disseminated intravascular coagulation. Decreased platelet production—most cases are acquired, with common or important causes being toxins (drugs, alcohol), nutritional deficiencies (folate or vitamin B12), bone marrow infiltration, and myelodysplastic syndrome. Disorders of platelet distribution and platelet sequestration include splenomegaly and hypersplenism, haemodilution, and extracorporeal circulation. Disorders of platelet function are usually acquired. The most common causes are medications and toxins, systemic disorders, and haematological diseases. Congenital disorders are a rare cause of symptomatic bleeding.

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