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

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    Default Platelets, Megathrombocyte, EDTA anticoagulated blood 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.[3] 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.[37] 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.[38] 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.
    Platelets, Megathrombocyte, EDTA anticoagulated blood attachment.php?s=793e652919d480e8b961b95024abf019&attachmentid=1443&d=1439750937

    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.


    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.

    Normal platelets. Blood film. Small blue staining cells with dark blue granules. Seven platelets are in this field compared to 70 red cells. This relationship depends on the optics and is variable from field to field. Commonly, there is an average of one platelet to 20 red cells on average in a normal blood film at 1000-fold magnification. This relates to a ratio of 250 x 109/L platelets to 5 x 1012/L red cells on average in normal blood. There is slight variation in size of the platelets in this field. About one in ten platelets in a normal blood film may be a megathrombocyte, defined as a platelet >2.5 mm diameter. This can be estimated as about greater than one-third the diameter of a normal red cell on a stained film from blood collected in Na2EDTA.

    Megathrombocyte. Blood film. The single platelet in this field is nearly the size of a red cell. Average normal sized platelets on a blood film are less than one-quarter the diameter of a red cell. The field also has fewer than expected platelets. This is a case of immune thrombocytopenia in which megathrombocytes are usually increased in inverse relationship to the platelet count. These are considered newly released platelets.

    Megathrombocyte. Blood film. Note platelets ranging from the size of red cells down to slightly large platelet size (normal average about one-fifth the diameter of a red cell). Case of thrombocythemia with increased platelets including pathologically large platelets.

    Platelet satellitism. Blood film. Platelets adherent to the neutrophil surface. This anomaly is often dependent on the effect of Na2EDTA exposure in the blood collection tube. In automated particle counts, this phenomenon may lead to the misdiagnosis of thrombocytopenia since the neutrophil with its accompanying platelets would fall above the upper size threshold for platelet counting and those platelets would be excluded from the count.

    Platelet satellitism. (A) Direct (non-anticoagulated) marrow film. No platelet satellitism. (B) A concentrated marrow film (Na2EDTA anticoagulated) from same specimen as in (A). Platelets adherent to the mature neutrophil surface only in the presence of Na2EDTA.

    Proplatelet. Platelets are released into the marrow sinus as long strings of platelets (megakaryocyte cytoplasmic strands). They normally separate into individual platelets prior to reaching the systemic ..

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    Last edited by Medical Photos; 08-16-2015 at 06:49 PM.

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