JAK2 Mutation
- Also Known As:
- Janus Kinase 2
- Formal Name:
- JAK2 V617F|JAK2 Exon 12 Mutation

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At a Glance
Why Get Tested?
To help diagnose bone marrow disorders known as myeloproliferative neoplasms (MPNs) in which the bone marrow produces too many of one or more types of blood cells
When To Get Tested?
When your health care practitioner suspects that you may have a bone marrow disorder, including polycythemia vera, essential thrombocythemia, or primary myelofibrosis
Sample Required?
A blood sample drawn from a vein in your arm or sometimes a sample of bone marrow
Test Preparation Needed?
None
What is being tested?
The Janus Kinase 2 gene, called JAK2 for short, provides instructions to cells for making the JAK2 protein. This protein promotes cell growth and division and is especially important for controlling blood cell production within the bone marrow. This test looks for mutations in JAK2 that are associated with bone marrow disorders caused by the production of too many blood cells.
The bone marrow disorders caused by JAK2 mutations are known as myeloproliferative neoplasms (MPNs) in which the bone marrow produces too many white blood cells, red blood cells, and/or platelets. Some of the MPNs most commonly associated with JAK2 mutations are:
- Polycythemia vera (PV)—the bone marrow makes too many red blood cells
- Essential thrombocythemia (ET)—there are too many platelet-producing cells (megakaryocytes) in the bone marrow
- Primary myelofibrosis (PMF), also known as chronic idiopathic myelofibrosis or agnogenic myeloid metaplasia—there are too many platelet-producing cells and cells that produce scar tissue in the bone marrow
The primary JAK2 test is JAK2 V617F, named for a mutation at a specific location in the JAK2 gene. JAK2 V617F mutation is acquired as opposed to inherited and results in the change of a single DNA nucleotide base pair. In JAK2, this kind of mutation, called a point mutation, replaces the normal amino acid valine (abbreviated V) with phenylalanine (abbreviated F). This amino acid change results in a JAK2 protein that is constantly “on,” leading to uncontrolled blood cell production.
Other mutations in the JAK2 gene are also associated with MPNs. Over 50 different mutations have been identified. There are tests available to detect mutations in JAK2 exon 12 and to identify other non-V617F mutations.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes a bone marrow aspiration and biopsy may be done to collect a sample for testing.
Common Questions
Related Content
On This Site
Tests: Bone Marrow Aspiration and Biopsy, Erythropoietin, Complete Blood Count, Blood Smear, Genetic Tests for Targeted Cancer Therapy, BCR-ABL1, CALR Mutation, Chromosome Analysis
Elsewhere On The Web
National Cancer Institute: Myeloproliferative Neoplasms
National Cancer Institute: Chronic Myeloproliferative Neoplasms
The Leukemia and Lymphoma Society: Myeloproliferative Neoplasms
MPN Research Foundation: Understanding MPNs
U.S. National Library of Medicine Genetics Home Reference: JAK2 gene
National Heart, Lung, and Blood Institute: What Is Polycythemia Vera?
View Sources
Sources Used in Current Review
Nagalla, S. and Besa, E. (2016 December 2 Updated). Polycythemia Vera Workup. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/205114-workup#c5. Accessed on 1/22/17.
Lal, A. (2016 November 10 Updated). Essential Thrombocytosis Workup. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/206697-workup#showall. Accessed on 1/22/17.
(© 1995–2017). JAK2 V617F Mutation Detection, Blood. Mayo Clinic Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/88715. Accessed on 1/22/17.
(© 1995–2017). JAK2 Exon 12 and Other Non-V617F Mutation Detection, Blood. Mayo Clinic Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/89189. Accessed on 1/22/17.
(2014 September Reviewed). Jak2 gene. Genetics Home Reference. Available online at https://ghr.nlm.nih.gov/gene/JAK2. Accessed on 1/22/17.
Kelley, T. and Salama, M. (2016 October Updated). Myeloproliferative Neoplasms – MPN. ARUP Consult. Available online at https://arupconsult.com/content/myeloproliferative-neoplasms. Accessed on 1/22/17.
Arber DA, Orazi A, Hasserjian R, et al. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood. 2016;127:2391-2405. Available online at http://www.bloodjournal.org/content/127/20/2391?sso-checked=true. Accessed February 2017.
Hofmann I. Myeloproliferative neoplasms in children. J Hematopathol. 2015;8:143-157.
Vainchenker W, Kralovics R. Genetic basis and molecular pathophysiology of classical myeloproliferative neoplasms. Blood. 2017;129:667-679.
Rumi E, Cazzola M. Diagnosis, risk stratification, and response evaluation in classical myeloproliferative neoplasms. Blood. 2017;129:680-692.
DeLario MR, Sheehan AM, Ataya R, et al. Clinical, histopathologic, and genetic features of pediatric primary myelofibrosis—an entity different from adults. Am J Hematol. 2012;87:461-464.
An W, Wan Y, Guo Y, et al. CALR mutation screening in pediatric primary myelofibrosis. Pediatr Blood Cancer. 2014;61:2256-2262.
Sources Used in Previous Reviews
(2007 May). Essential or Primary Thrombocythemia. The Leukemia and Lymphoma Society [On-line information]. PDF available for download at http://www.leukemia-lymphoma.org/attachments/National/br_1178803674.pdf. Accessed July 2009.
(2009 February). What Is Polycythemia Vera? National Heart, Lung, and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/poly/poly_whatis.html. Accessed July 2009.
Beals, J. (2009 March 16) JAK2 Haplotypes Influence Susceptibility to Myeloproliferative Neoplasms. Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/589655. Accessed July 2009.
McMahon, C. et. al. (2007 May 25). JAK2 V617F Mutation in Patients With Catastrophic Intra-abdominal Thromboses. Medscape from American Journal of Clinical Pathology [On-line information]. Available online at http://www.medscape.com/viewarticle/556664. Accessed July 2009.
Tan, A. et. al. (2007 July 23). A Simple, Rapid, and Sensitive Method for the Detection of the JAK2 V617F Mutation. Medscape from American Journal of Clinical Pathology [On-line information]. Available online at http://www.medscape.com/viewarticle/558906. Accessed July 2009.
Vannucchi, A. et. al. (2009 March 23). Treatment Options for Essential Thrombocythemia and Polycythemia Vera. Medscape from Expert Review of Hematology [On-line information]. Available online at http://www.medscape.com/viewarticle/589735. Accessed July 2009.
(2007 March). JAK2 c.1849G>T (V617F) Mutation Quantification by Real-Time PCR. ARUP Technical Bulletin [On-line information]. PDF available for download through http://www.aruplab.com. Accessed July 2009.
(2007 March). JAK2 (V617F) Mutation by PCR. ARUP Technical Bulletin [On-line information]. PDF available for download through http://www.aruplab.com. Accessed July 2009.
Check, W. (2008 September). Class action for myeloproliferative disorders. CAP Today [On-line information]. Available online through http://www.cap.org. Accessed July 2009.
(13 Feb. 2012). Tefferi, Ayalew. Polycythemia vera and essential thrombocythemia: 2012 update on diagnosis, risk stratification, and management. American Journal of Hematology Continuing Education Series. Available online through http://onlinelibrary.wiley.com. Accessed June 2013.
(April 2013). Classic BCR-ABL1-negative Myeloproliferative Neoplasms. Arup Laboratories. PDF available for dowload at http://www.aruplab.com/guides/ug/tests/iconpdf_383.pdf. Accessed June 2013.
(Dec. 8, 2012). Kiladjian, Jean-Jacques. The spectrum of JAK2-Positive myeloproliferative neoplasms. American Society of Hematology Education Book. Available online at http://asheducationbook.hematologylibrary.org/content/2012/1/561.full. Accessed June 2013.
(Updated May 2013). Myeloproliferative Neoplasms. Arup Consult. Available online at http://www.arupconsult.com/Topics/MyeloproliferativeNeoplasms.html. Accessed June 2013.
(Reviewed Dec. 2011). JAK2. National Library of Medicine. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/gene/JAK2. Accessed June 2013.
(Reviewed Dec. 2011). Essential thrombocythemia. National Library of Medicine. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/condition/essential-thrombocythemia. Accessed June 2013.
Vainchenker, William, et al. (June 7, 2011). New mutations and pathogenesis of myeloproliferative neoplasms. Blood. American Society of Hematology. PDF available for download at http://bloodjournal.hematologylibrary.org/content/118/7/1723.full.pdf. Accessed June 2013.
(Updated March 2013). Janus Kinase 2. Online Mendelian Inheritance in Man (OMIM). Available online at http://omim.org/entry/147796. Accessed June 2013.
(2012 Sept.) Essential Thrombocythemia. Mayo Clinic. Available online at http://www.mayoclinic.com/health/thrombocythemia/DS01087/DSECTION=symptoms. Accessed June 2013.
(2011 Dec.) Myelofibrosis. Mayo Clinic. Available online at http://www.mayoclinic.com/health/myelofibrosis/DS00886/DSECTION=symptoms. Accessed June 2013.
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