What does it mean when platelets are high in the blood?

Thanks for asking! There are 2 major processes associated with thrombocytosis (high platelet count), namely (1) essential or primary; (2) reactive or secondary. Primary causes: essential thrombocytosis and other myeloproliferative disorders. Secondary causes include inflammation, surgery, hyposplenism (decreased platelet breakdown due to reduced function of the spleen), splenectomy, iron deficiency anemia, ...Etc.