JAK2 and polycythemia: The complexity and variability of the decision-making processes involved in managing erythrocytosis were underscored by an international survey of 134 myeloproliferative neoplasm (MPN) physicians evaluating standard practice in erythrocytosis [10]; in this regard, while first-line assessments were relatively consistent (JAK2, EPO testing), second-line investigations were markedly heterogeneous.