Algorithm for diagnosis of MPN. CML indicates chronic myeloid leukemia; LDH, lactate dehydrogenase; and MDS, myelodysplasia. *Clear evidence of erthrocytosis refers to either hematocrit >0.56 in women or 0.60 in men, elevated RBC mass, or, in the absence of a secondary cause, low erythropoietin, JAK2 exon 12- or 14-positive, and hematocrit >2.5 SDs outside of the normal range.