At a Glance
Why Get Tested?
When to Get Tested?
When your doctor suspects that you may have a bone marrow disorder, including polycythemia vera, essential thrombocythemia, or primary myelofibrosis
A blood sample drawn from a vein in your arm; sometimes a sample of bone marrow
Test Preparation Needed?
The Test Sample
What is being tested?
The Janus Kinase 2 or JAK2 gene provides instructions for making the JAK2 protein, which promotes cell growth and division, and is especially important for controlling blood cell production from stem cells located within the bone marrow. This test looks for mutations in JAK2 that are associated with bone marrow disorders caused by an overproduction of blood cells.
The bone marrow disorders caused by JAK2 mutations are known as myeloproliferative neoplasms (MPNs), where the bone marrow overproduces white blood cells, red blood cells, and/or platelets. Some of the MPNs most commonly associated with JAK2 are: polycythemia vera (PV), where bone marrow makes too many red blood cells; essential thrombocythemia (ET), where there are too many platelet-producing cells (megakaryocytes) in the bone marrow; and primary myelofibrosis (PMF), also known as chronic idiopathic myelofibrosis or agnogenic myeloid metaplasia, where 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, leads to a change in the protein building block that the gene codes for, replacing the normal amino acid valine (V) with phenylalanine (F). This amino acid change results in a JAK2 protein that is constantly "on," leading to uncontrolled blood cell production.
As many as 95% of people with PV and 50-75% of people with ET or PMF are positive for the JAK2 V617F mutation. Additionally, the mutation is also infrequently detected in people with chronic myelomonocytic leukemia (CMML), primary acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and chronic myeloid leukemia (CML).
Mutations in other coding portions (called exons; they code for proteins) of the JAK2 gene are also associated with MPNs. There are tests to detect changes in JAK2 exon 12. Two to five percent of people with PV have an exon 12 mutation.
The presence of a JAK2 mutation helps a health care provider make a definitive diagnosis of MPN (PV, ET or PMF), but the absence of a JAK2 mutation does not rule out MPN. In 2008, the World Health Organization (WHO) revised its diagnostic criteria for PV and ET, adding the presence of JAK2 mutation as a criterion. However, consensus has not yet been achieved for the optimal diagnostic criteria for PV.
The finding of a JAK2 mutation associated with uncontrolled blood cell growth in MPNs also suggests a possible therapeutic approach to some MPNs. As an example, one JAK2 inhibitor has been approved for the treatment of intermediate and high risk myelofibrosis.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Bone marrow can also be used to detect the mutation.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
(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 through http://www.aruplab.com. 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 through asheducationbook.hematologylibrary.org. Accessed June 2013.
(Updated May 2013). Myeloproliferative Neoplasms. Arup Consult. Available online at http://www.arupconsult.com/Topics/MyeloproliferativeNeoplasms.html through http://www.arupconsult.com. Accessed June 2013.
(Reviewed Dec. 2011). JAK2. National Library of Medicine. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/gene/JAK2 through http://ghr.nlm.nih.gov. 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 through http://ghr.nlm.nih.gov. 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 through http://bloodjournal.hematologylibrary.org. Accessed June 2013.
(Updated March 2013). Janus Kinase 2. Online Mendelian Inheritance in Man (OMIM). Available online at http://omim.org/entry/147796 through http://omim.org. Accessed June 2013.
(2012 Sept.) Essential Thrombocythemia. Mayo Clinic. Available online at http://www.mayoclinic.com/health/thrombocythemia/DS01087/DSECTION=symptoms through http://www.mayoclinic.com. Accessed June 2013.
(2011 Dec.) Myelofibrosis. Mayo Clinic. Available online at http://www.mayoclinic.com/health/myelofibrosis/DS00886/DSECTION=symptoms through http://www.mayoclinic.com. Accessed June 2013.
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 through http://www.leukemia-lymphoma.org. 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 through http://www.nhlbi.nih.gov. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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.