What is the role of lab testing in the diagnosis of immune thrombocytopenic purpura (ITP)?

Updated: Apr 22, 2018
  • Author: Craig M Kessler, MD, MACP; Chief Editor: Srikanth Nagalla, MBBS, MS, FACP  more...
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Answer

On complete blood cell count, isolated thrombocytopenia is the hallmark of ITP. Anemia and/or neutropenia may indicate other diseases. Findings on peripheral blood smear are as follows:

  • The morphology of red blood cells (RBCs) and leukocytes is normal

  • The morphology of platelets is typically normal, with varying numbers of large platelets

  • If most of the platelets are large, approximating the diameter of red blood cells, or if they lack granules or have an abnormal color, consider an inherited platelet disorder

Many children with acute ITP have an increased number of normal or atypical lymphocytes on the peripheral smear, reflecting a recent viral illness. Clumps of platelets on a peripheral smear prepared from ethylenediaminetetraacetic acid (EDTA)–anticoagulated blood are evidence of pseudothrombocytopenia. [3] This diagnosis is established if the platelet count is normal when repeated on a sample from heparin-anticoagulated or citrate-anticoagulated blood.


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