Mutation screening for JAK2V617F: when to order the test and how to interpret the results.

With the application of adequately sensitive tests, it is now becoming evident that more than 90% of patients with conventionally-defined polycythemia vera (PV) carry the somatic JAK2V617F mutation in their granulocytes. However, the specific mutation is also found in other classic and atypical myeloproliferative disorders (MPD), albeit at a lesser frequency. In contrast, JAK2V617F has not been reported in patients with either reactive myeloproliferation or lymphoid disorders. Therefore, mutation screening for JAK2V617F can be considered as a myeloid-specific clonality assay and it is diagnostically most useful in the evaluation of "polycythemia".