Our approach to the differential diagnosis of thrombocytosis. For the analysis of JAK2/CALR/MPL mutations status, we use granulocyte DNA and perform the following tests sequentially: (1) a quantitative polymerase chain reaction–based allelic discrimination assay for JAK2 (V617F) with a sensitivity of <0.1%; (2) if JAK2 (V617F) is absent, Sanger sequencing for detection of CALR exon 9 indels; (3) if JAK2 (V617F) is absent and CALR exon 9 is wild type, a high-resolution melt assay for detection of MPL exon 10 mutations followed by Sanger sequencing in case of mutant pattern. H&E, hematoxylin and eosin.