Classification of MPNs as adapted from the WHO 2017 criteria.¹  LDH, lactate dehydrogenase; MKC, megakaryocyte. 2016 WHO grading of myelofibrosis: MF-0, scattered linear reticulin with no intersections (crossovers) corresponding to normal bone marrow; MF-1, loose network of reticulin with many intersections, especially in perivascular areas; MF-2, diffuse and dense increase in reticulin with extensive intersections, occasionally with focal bundles of thick fibers, mostly consistent with collagen and/or focal osteosclerosis; MF-3, diffuse and dense increase in reticulin with extensive intersections and course bundles of thick fibers consistent with collagen, usually associated with osteosclerosis.