At a Glance
Why Get Tested?
To help diagnose myeloproliferative neoplasms (MPNs)
When to Get Tested?
When your doctor suspects that you may have polycythemia vera, essential thrombocythemia, or primary myelofibrosis
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
The JAK2 tests detect the presence of acquired mutations in the Janus Kinase 2 (JAK2) gene. JAK2 mutations are not inherited; they are acquired, occurring for unknown reasons at some point in an affected person's life. Recent research has established an association between changes in the JAK2 gene and several myeloproliferative neoplasms (MPNs). MPNs are a group of bone marrow disorders that are characterized by an overproduction of one or more types of abnormal blood or fiber cells in the bone marrow. MPNs that have been associated most strongly with JAK2 include polycythemia vera (PV), essential thrombocythemia (ET), and agnogenic myeloid metaplasia (primary myelofibrosis, PMF).
The principal JAK2 test is called JAK2 V617F. It detects a mutation at a specific place on the JAK2 gene termed a point mutation. This causes a change in the protein produced by the gene at amino acid 617 replacing the normal valine (V) with phenylalanine (F). This change activates the JAK2 gene and promotes uncontrolled cellular growth. As many as 90% of people with PV and 50% of people with ET or PMF may be positive for the JAK2 V617F mutation.
Other JAK2 mutations are also associated with some cases of MPNs. These tests detect changes in certain portions (exons) of the gene. These mutations affect JAK2 exon 12 and JAK2 exon 13.
In 2008, the World Health Organization (WHO) updated its diagnostic criteria for PV and ET, adding as a major criterion the "presence of the JAK2 V617F or other functionally similar mutations, such as JAK2 exon 12 mutations." This update has not been accepted by everyone in the medical community, but JAK2 testing has begun to be used to help diagnose MPNs.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
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.
Ask a Laboratory Scientist
This form enables you to ask specific questions about your tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. If your questions are not related to your lab tests, please submit them via our Contact Us form. Thank you.
* indicates a required field
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.
(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 at http://www.aruplab.com/Testing-Information/resources/TechnicalBulletins/JAK2%20c.1849G-T%20(V617F)%20Mutation%20Quantification%20by%20Real-Time%20PCR%20-%20March%202007.pdf#xml=http://websearch-vrt.aruplab.net/isysquery/8edd8faa-25d9-47cc-b7d7-60193abd52e4/3/hilite/ 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 at http://www.aruplab.com/Testing-Information/resources/TechnicalBulletins/JAK2%20(V617F)%20Mutation%20by%20PCR%20-%20March%202007.pdf#xml=http://websearch-vrt.aruplab.net/isysquery/8edd8faa-25d9-47cc-b7d7-60193abd52e4/4/hilite/ through http://www.aruplab.com. Accessed July 2009.
Check, W. (2008 September). Class action for myeloproliferative disorders. CAP Today [On-line information]. Available online at http://www.cap.org/apps/cap.portal?_nfpb=true&cntvwrPtlt_actionOverride=%2Fportlets%2FcontentViewer%2Fshow&_windowLabel=cntvwrPtlt&cntvwrPtlt%7BactionForm.contentReference%7D=cap_today%2F0908%2F0908_class_action_2.html&_state=maximized&_pageLabel=cntvwr through http://www.cap.org. Accessed July 2009.