Haematological disorders

Myeloproliferative disorders—qualitative platelet disorders occur in association with a prolonged bleeding time and clinical bleeding in MPD. Includes abnormal morphology with decreased granules, acquired storage pool defects, abnormalities of platelet glycoproteins, receptors and arachidonic acid metabolism. Haemorrhage (mucocutaneous) and thrombosis can occur in the same patient. Neither platelet function tests nor degree of thrombocytosis correlates well with risks of bleeding or thrombosis. An increased whole blood viscosity in patients with polycythaemia is clearly related to risk of haemorrhage. There is evidence that that lowering an elevated platelet count to <600 x 109/L is associated with a reduced risk of thrombosis. Hydroxyurea is effective. The role of anagrelide is not yet clear. In patients with polycythaemia rubra vera the haematocrit should be kept below 0.44 (9) or 0.47 (9). (ffl p243).

Myelodysplasia and leukaemia—abnormalities of platelet morphology and in vitro aggregation occur in these disorders but haemorrhagic problems are commonly due to thrombocytopenia.

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