The JAK2 V617F mutation analysis by polymerase chain reaction (PCR) is a molecular test designed to detect a specific point mutation (valine-phenylalanine substitution at position 617) in the Janus Kinase 2 (JAK2) gene. This mutation is found in the vast majority of patients with polycythemia vera and in a significant proportion of patients with primary myelofibrosis and essential thrombocytosis, and is considered a key diagnostic criterion.