An increased proportion of MPN-associated driver mutations (JAK2, CALR, MPL) was observed in individuals with more severe thrombocytosis (ie, platelet count >450 × 109/L) (44.6% vs 0.0%; P < 0.001), but not for those with mild thrombocytosis (ie, platelet count 400–450 × 109/L; 6.0% vs 1.7%; P = 0.171; Suppl. Here, CALR is linked to Thrombocytosis.