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(Circulation. 2000;101:938.)
© 2000 American Heart Association, Inc.
Images in Cardiovascular Medicine |
Abciximab-Associated Pseudothrombocytopenia
From The University of Vermont College of Medicine, Burlington.
Correspondence to Michael B. Holmes, MD, Cardiovascular Division, The University of Vermont College of Medicine, McClure 1, Fletcher Allen Health Care, Burlington, VT 05401. E-‘mail michael.holmes@vtmednet.org
A60-year-old
woman was transferred for coronary angiography after a
non–Q-wave myocardial infarction. She was treated with aspirin,
metoprolol, unfractionated heparin, and abciximab administered as a
weight-based bolus followed by infusion. A complete blood count in
blood anticoagulated with EDTA (purple-top Vacutainer) was obtained
shortly after her arrival in the catheterization
laboratory, 4 hours after the abciximab bolus. The reported
platelet count had decreased from 440 000/mL to 21 000/mL.
Examination of the peripheral blood smear revealed
prominent clumping of the platelets
(Figure
, bottom). Repeat analysis
performed in the catheterization laboratory in blood
anticoagulated with citrate (blue-top Vacutainer) demonstrated a true
platelet count of 320 000/mL associated with a normal appearance
of the peripheral smear (Figure, top). She
subsequently underwent angiography without delay or complications.
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Pseudothrombocytopenia is an artifactual clumping of
platelets in vitro without clinical significance. Most frequently,
EDTA alters the conformation of the platelet surface
glycoprotein IIb such that a neoepitope is exposed that is
recognized by autologous antibodies. The incidence of
pseudothrombocytopenia in the general population is 
0.1%. The
incidence of pseudothrombocytopenia was 1.1% in patients receiving
abciximab as a bolus plus infusion in the EPIC trial, whereas the
incidence of true acute thrombocytopenia was 2.7%. Thus,
pseudothrombocytopenia is an important etiology of
thrombocytopenia to consider in patients receiving abciximab.
Evaluation of the automated platelet count and peripheral smear in blood anticoagulated in citrate can distinguish pseudothrombocytopenia from heparin-induced thrombocytopenia and true thrombocytopenia related to abciximab. The distinction is critical because with pseudothrombocytopenia, thrombotic or hemorrhagic risk is not increased, antithrombotic and antiplatelet therapy can be continued, and invasive procedures can be performed.
Footnotes
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
Circulation encourages readers to submit cardiovascular images to Dr Hugh A. McAllister, Jr, St Luke’s Episcopal Hospital and Texas Heart Institute, 6720 Bertner Ave, MC1-267, Houston, TX 77030.
(Circulation. 2000;101:938-939.)
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