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Thread: Megathrombocyte, EDTA anticoagulated blood, ET picture - blood histology atlas

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    Default Megathrombocyte, EDTA anticoagulated blood, ET picture - blood histology atlas

    Laboratory Studies
    The workup for immune thrombocytopenic purpura (ITP) starts with a complete blood cell (CBC) count. The hallmark of ITP is isolated thrombocytopenia; anemia and/or neutropenia may indicate other diseases

    On peripheral blood smear, the morphology of red blood cells (RBCs) and leukocytes is normal. The morphology of platelets is typically normal, with varying numbers of large platelets. Some persons with acute ITP may have megathrombocytes or stress platelets, reflecting the early release of megakaryocytic fragments into the circulation. If most of the platelets are large, approximating the diameter of RBCs, or if they lack granules or have an abnormal color, consider an inherited platelet disorder.

    Clumps of platelets on a peripheral smear prepared from ethylenediaminetetraacetic acid (EDTA)–anticoagulated blood are evidence of pseudothrombocytopenia. The diagnosis of this type of pseudothrombocytopenia is established if the platelet count is normal when repeated on a sample from heparin-anticoagulated or citrate-anticoagulated blood.

    In patients who have risk factors for HIV infection, a blood sample should be tested with an enzyme immunoassay for anti-HIV antibodies During the acute HIV retroviral syndrome, the results of the anti-HIV assay may be negative. In this situation, a polymerase chain reaction for HIV DNA is more reliable than the anti-HIV assay.

    Assays for platelet antigen–specific antibodies, platelet-associated immunoglobulin, or other antiplatelet antibodies are available in some medical centers and certain mail-in reference laboratories. The reliability of the results of a platelet antibody test is highly specific to the laboratory used. A negative antiplatelet antibody assay result does not exclude the diagnosis of ITP. The authors do not recommend this test as part of the routine evaluation. Testing for antiplatelet antibodies is not required to diagnose ITP.

    In selected women, the medical history may suggest a chronic, recurrent, multisystemic illness with vague, generalized signs or symptoms, such as recurrent, multiple, painful, tender, or swollen joints. In such cases, a negative antinuclear antibody (ANA) result is useful in diagnosing ITP if the patient's thrombocytopenia becomes chronic and resistant to treatment.

    If anemia and thrombocytopenia are present, a positive direct antiglobulin (Coombs) test result may help establish a diagnosis of Evans syndrome.

    Studies from Italy and Japan indicate that many persons with ITP have H pylori gastric infections and that eradication of H pylori results in increased platelet counts. In the United States and Spain, however, the prevalence of H pylori infections does not appear to be increased in persons with ITP, and eradication of H pylori has not increased platelet counts. Therefore, routine testing for H pylori infections in adults and children with ITP is not recommended.
    Megathrombocyte, EDTA anticoagulated blood, picture attachment.php?s=d4b8b052b66609e4cb73d2f4172cfe4b&attachmentid=1442&d=1439749033

    Bone marrow aspirate
    The cellularity of the aspirate and the morphology of erythroid and myeloid precursors should be normal. The number of megakaryocytes may be increased. Because the peripheral destruction of platelets is increased, megakaryocytes may be large and immature, although in many cases the megakaryocyte morphology is normal. Older patients require a careful examination of megakaryocyte morphology to exclude an early myelodysplastic syndrome.

    Bone marrow biopsy
    Sections of a needle biopsy specimen or marrow clot should reveal normal marrow cellularity, without evidence of hypoplasia or increased fibrosis.

    Splenic evaluation
    The spleen reveals no specific findings. In adults, the microscopic finding of extramedullary hematopoiesis is atypical and indicates myeloid metaplasia. Spleens removed from patients with immune thrombocytopenic purpura (ITP) should be carefully examined for a primary splenic lymphoma or granuloma or other signs of an undiagnosed infectious disease.

    Pathophysiology
    In immune thrombocytopenic purpura (ITP), an abnormal autoantibody, usually immunoglobulin G (IgG) with specificity for one or more platelet membrane glycoproteins (GPs), binds to circulating platelet membranes.
    Autoantibody-coated platelets induce Fc receptor-mediated phagocytosis by mononuclear macrophages, primarily but not exclusively in the spleen. The spleen is the key organ in the pathophysiology of ITP, not only because platelet autoantibodies are formed in the white pulp, but also because mononuclear macrophages in the red pulp destroy immunoglobulin-coated platelets.

    If bone marrow megakaryocytes cannot increase production and maintain a normal number of circulating platelets, thrombocytopenia and purpura develop. Impaired thrombopoiesis is attributed to failure of a compensatory increase in thrombopoietin and megakaryocyte apoptosis.

    Etiology
    In children, most cases of immune thrombocytopenic purpura (ITP) are acute, manifesting a few weeks after a viral illness. In adults, most cases of ITP are chronic, manifesting with an insidious onset, and occur in middle-aged women. These clinical presentations suggest that the triggering events may be different. However, in both children and adults, the cause of thrombocytopenia (destruction of antibody-coated platelets by mononuclear macrophages) appears to be similar.

    United States
    The annual incidence of immune thrombocytopenic purpura (ITP) is estimated to be five cases per 100,000 children and two cases per 100,000 adults,but these data are not from large population-based studies. Most cases of acute ITP, particularly in children, are mild and self-limited and may not receive medical attention. Therefore, estimated incidences of ITP are difficult to determine and are likely to understate the full extent of the disease. The age-adjusted prevalence of ITP in Maryland was reported as 9.5 per 100,000 persons by Segal and Powe.

    References:
    http://emedicine.medscape.com/articl...58-overview#a6











    Last edited by Medical Photos; 08-16-2015 at 06:17 PM.

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