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- Larry D Brace, PhD⇑
- Address for correspondence: Larry Brace PhD, Professor Emeritus, University of Illinois at Chicago, 11285 Plainfield Road, Indian Head Park IL 60525. (708) 246-7150. lbrace{at}uic.edu.
Upon completion of this article, the reader will be able to:
list the inherited forms of thrombocytopenia and distinguish disorders of production from disorders of consumption.
recall the hallmark laboratory findings of chronic and acute immune thrombocytopenia purpura.
test for heparin-induced thrombocytopenia with thrombosis.
distinguish thrombocytopenia-induced mucocutaneous bleeding from anatomic bleeding.
describe the mechanism of drug-induced thrombocytopenia and the means for its detection and cure.
distinguish between thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome.
Extract
Thrombocytopenia is a decrease in circulating platelet count. The typical reference range is approximately 150,000 to 450,000/μL. Thrombocytopenia (platelet count <150,000/μL) is the most common cause of mucocutaneous bleeding, characterized by petechiae, purpura, ecchymoses, epistaxis, hematemesis, and menorrhagia. The primary pathophysiologic processes in thrombocytopenia are decreased platelet production, accelerated platelet destruction, and abnormal platelet distribution or sequestration (Table 1).
It is unusual for bleeding to occur when the platelet count is greater than 50,000/μL, and patients with platelet counts of 20,000/μL may have few bleeding symptoms. Patients with platelet counts less than 10,000/μL are at high risk for a serious spontaneous hemorrhagic episode.
Congenital megakaryocytic hypoplasia Megakaryocytic hypoplasia (decrease in bone marrow megakaryocytes) is seen in thrombocytopenia with absent radii (TAR), Wiskott-Aldrich syndrome, Bernard-Soulier syndrome, and May-Hegglin anomaly. Although thrombocytopenia is a feature of Bernard-Soulier syndrome and Wiskott-Aldrich syndrome, the primary abnormality is qualitative so these are discussed separately.
May-Hegglin anomaly is a rare autosomal dominant disorder whose exact frequency is unknown. Platelets are 20 μm in diameter and Döhle bodies are present in neutrophils (Figure 1). Other than their increased diameter, platelet morphology is normal. Thrombocytopenia is present in about one third to one half of patients. Platelet function in response to platelet activating agents is normal. In some patients, megakaryocytes are increased in number and have abnormal ultrastructure. A mutation in the MYH9 gene that encodes for non-muscle myosin heavy chain, a cytoskeletal protein in platelets, may be responsible for the abnormal platelet diameter.1-3 Most…
ABBREVIATIONS: DIC = disseminated intravascular coagulation; HELLP syndrome = microangiopathic hemolysis, elevated liver enzymes, and a low platelet count; HIT = heparin-induced thrombocytopenia; HUS = hemolyticuremic syndrome; HUS = hemolytic-uremic syndrome; ITP = immune thrombocytopenic purpura; PF4 = platelet factor 4; TAR = thrombocytopenia with absent radii; TTP = thrombotic thrombocytopenic purpura; ULVWF = unusually large von Willebrand factor; VWF = von Willebrand factor.
Upon completion of this article, the reader will be able to:
list the inherited forms of thrombocytopenia and distinguish disorders of production from disorders of consumption.
recall the hallmark laboratory findings of chronic and acute immune thrombocytopenia purpura.
test for heparin-induced thrombocytopenia with thrombosis.
distinguish thrombocytopenia-induced mucocutaneous bleeding from anatomic bleeding.
describe the mechanism of drug-induced thrombocytopenia and the means for its detection and cure.
distinguish between thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome.
- © Copyright 2007 American Society for Clinical Laboratory Science Inc. All rights reserved.
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