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JAK2 Mutation Screening

In early 2005, several groups of investigators reported a somatic acquired point mutation in the JAK2 (Janus kinase 2) protein in the blood and bone marrow of patients with BCR/ABL-negative chronic myeloproliferative disorders. JAK2 is a tyrosine kinase which plays an important role in normal hematopoietic growth factor signaling. A mutation at V617F results in a hyperactive kinase that is believed to allow erythropoietin independent survival of the myeloid stem cell.

Using sensitive assays, the JAK2 mutation can be detected in approximately 90-95% of cases of polycythemia vera, 50-70% of patients with essential thrombocythemia, and 40-50% of cases of idiopathic myelofibrosis. The mutation has also been described in rare cases of myelodysplastic syndromes, acute myeloid leukemia, systemic mastocytosis and hypereosinophilic syndrome. It is specific for diagnosis of a clonal myeloid lineage proliferative disorder. The mutation has not been described in BCR/ABL-positive chronic myeloid leukemia, any acute or chronic lymphoid disorders, any healthy persons, or any patient with secondary polycythemia or a reactive blood count elevation. The JAK2 test promises to be very useful in distinguishing between clonal myeloproliferative disorders and reactive cellular proliferations.

Indications for the assay include the following:

  • Evaluation of polycythemia - the test should be ordered in addition to serum erythropoietin level.
  • Evaluation of an elevated platelet count, clinically not consistent with reactive thrombocytosis.
  • Unusual thrombotic events including abdominal or cerebral thrombosis or arterial events at a young age, which may be a presenting sign of an underlying chronic myeloproliferative disorder.

It is important to keep in mind that a positive JAK2 mutation is not specific for a particular sub-type of myeloproliferative disorder, and must be correlated with other clinical and laboratory findings for definitive diagnosis. Furthermore, a negative result does not exclude the presence of a chronic myeloproliferative disorder or other neoplastic disorder.

JAK2 and BCR-ABL PCR testing should be considered complementary in the workup of myeloproliferative disorders. A few cases of dual positivity for both mutations have been reported.

Sample requirement is one lavender-top tube containing at least 3mL of peripheral blood or bone marrow. The assay will be performed twice a week.

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