Elevated platelet count
Thrombocytosis is defined as a platelet count >450 x 109/L. May be due to a primary myeloproliferative disorder (MPD) or a secondary reactive 20 feature. If the platelet count is markedly elevated a patient with a myeloproliferative disorder has a risk of haemorrhage (due to the production of dysfunctional platelets), or thrombosis, or both. The patient's history may reveal features of the condition to which the elevated platelet count is secondary. Clinical examination may provide similar clues or reveal the presence of palpable splenomegaly which suggests a myeloproliferative disorder. FBC may provide useful information: marked leucocytosis with left shift (in the absence of a history of infection), basophilia or an elevated haematocrit and red cell count are highly suggestive of a myeloproliferative disorder when associated with thrombocytosis. Unusual for reactive thrombocytosis to cause a platelet count >1000 x 109/L. Note: platelet counts below this may occur in myeloproliferative disorders.