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The upper limit of a normal platelet count is usually between 350 × 109/L and 450 × 109/L depending on the clinical laboratory and specific method used.
Table 74–1 presents the major causes of elevation of the platelet count above the normal limit.
Reactive thrombocytosis may persist for prolonged periods and resolve only with resolution of the underlying disorder.
Thrombocytosis after recovery from thrombocytopenia (“rebound”) usually peaks in 10 to 14 days.
The platelet count after splenectomy may reach 1000 × 109/L or more within the first week and return to normal within about 2 months. Severe or persistent postsplenectomy thrombocytosis may be a result of persistent iron deficiency anemia or unmasking of primary thrombocythemia.
There is no convincing evidence that therapy to reduce the platelet count or interfere with platelet function is of benefit in reactive thrombocytosis, with the possible exception of severe postsplenectomy thrombocytosis in patients with persistent hemolytic anemia, in which case aspirin therapy might be considered.
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For a more detailed discussion, see Kenneth Kaushansky: Reactive Thrombocytosis, Chap. 119 in Williams Hematology, 9th ed.