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Thread: Small Platelets, Megathrombocytes picture - blood histology atlas

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    Default Small Platelets, Megathrombocytes picture - blood histology atlas

    Summary
    Human platelets have been separated into heavy and light populations by differential centrifugation in specific density media. The heavy-platelet population has an average volume approximately 2–2.4-fold that of the light-platelet population. All eleven enzymes of the Embden-Meyerhof pathway were examined in both platelet populations. Six of the eleven were found to have a twofold greater content/g wet weight in heavy platelets compared to light platelets. Three of these six: hexokinase, phosphofructokinase, and glyceraldehyde-3-P-dehydroge-nase were found to be rate-limiting for glycolysis. The reductive capacity of heavy vs. light platelets was also examined. Heavy platelets contained 1.9-fold greater GSH, 1.7-fold greater DPNH, and 1.2-fold greater TPNH than light platelets. Heavy platelets also contained 1.8-fold less lipid peroxidation products than light platelets and were 2.4-fold more resistant to lipid peroxidation catalysed by 0.1 mM FeCl3.

    Kinetic studies in humans with Se75-selenomethionine revealed that heavy-large platelets were young platelets, recently released from the bone marrow, and suggested a transition of heavy-large platelets to lighter-smaller platelets.

    Clinical studies in humans revealed the usefulness of the measurement of the percentage of large platelets (or megathrombocytes) in estimating platelet turnover. An excellent correlation was found between the percentage of megathrombocytes on EDTA peripheral smear (and as determined by volume with Coulter Counter) and the number of megakaryocytes in the bone marrow in all platelet disorders examined with low or normal platelet counts, r=0.70 P < 0.001, except in megaloblastic anemia. In megaloblastic anemia, an increase in the percentage of megathrombocytes was usually found, but in the absence of increased megakaryocyte number. Increased megathrombocyte number (% megathrombocytes X platelet count) could be used to predict compensated thrombocytolytic states: normal platelet counts in the presence of increased platelet turnover. This was detectable in 84 patients. Platelet survival studies with DFP32 were obtained in eight of these patients and found to be exponential and significantly shortened in all eight. Megathrombocyte number was also examined in various clinical disorders (with normal platelet counts) in which increased platelet turnover might be suspected. Significant elevations were noted in SLE (68%), rheumatic heart disease with severe valvular damage (63%), disseminated intravascular coagulation (60%), chronic autoimmune thrombocytopenic purpura “in remission” (55%), and diabetes mellitus with retinopathy (47%).

    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. (See IV.A.2.)
    Small Platelets, Megathrombocytes picture blood attachment.php?s=3582e370dacaa7fff3811223033bea8b&attachmentid=1444&d=1439751471

    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 ...

    A rapid technique suitable for routine laboratory use for determining the percentage of large platelets in the peripheral blood is described. In 50 haematologically normal subjects, megathrombocytes (platelets with a volume of 16-33 fl) constituted 3.0-16.6% (mean +/- 2 SD) of the platelet count. Of the 10 patients examined with immune thrombocytopenic purpura, an increased percentage of megathrombocytes (mean 26.6%) was found in all with severe thrombocytopenia, and in 6 of 8 (mean 19.8%) with moderate thrombocytopenia; the percentages were not influenced by prior splenectomy. Six of 12 patients with severe hypomegakaryocytic thrombocytopenia had an increased percentage of large platelets (mean 15.9%), as did one of 21 patients (mean 9.9%) with moderate thrombocytopenia of simimlar aetiology. When patients with nearly identical platelet counts were compared, the mean percentage of megathrombocytes was greater in immune than in hypomegakaryocytic thrombocytopenia for both severe (t=3.17, P less than 0.01) and moderate (t=4.5, P less than 0.001) thrombocytopenia. An increased percentage of large platelets (mean 21.9%) was found in 6 to 8 patients with disseminated intravascular coagulation, in 7 of 20 (mean 15.8%) with chronic myeloproliferative disorders and in one of 15 (mean 8.8%) with reactive thrombocytosis. Determination of the percentage of megathrombocytes by this technique assists in differentiating immune thrombocytopenia from hypomegakaryocytic thrombocytopenia, in diagnosing mild disseminated intravascular coagulation, and in determining whether thrombocytosis is reactive or a consequence of a myeloproliferative disorders.

    References:
    A rapid method for assessing megathrombocytes: its application to thrombocytotic and acquired thrombocytopenic states.
    AccessMedicine | Content

    BIOCHEMICAL and CLINICAL ASPECTS OF MEGATHROMBOCYTES - Karpatkin - 2006 - Annals of the New York Academy of Sciences - Wiley Online Library











    Last edited by Medical Photos; 08-16-2015 at 06:57 PM.

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