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Understanding the JAK2 Laboratory Test

written by: R. Elizabeth C. Kitchen•edited by: Lamar Stonecypher•updated: 10/29/2009

This article discusses the JAK2 laboratory test.

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    JAK2 is a protein tyrosine kinase and a gene product. It is essential for gamma interferon responses and is associated with the prolactin receptor. It is a coding gene and its full name is janus kinase 2.

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    How is this Test Used?

    This test is most often done when trying to establish a diagnosis of myeloproliferative disorders, agnogenic myeloid metaplasia, essential thrombocythemia, or polycythemia vera. These disorders are often referred to as MPD. It is often used in combination with other tests like an erythropoietin test. It may be used as a follow-up test if a patient presents an increased platelet or hemoglobin count.

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    When is this Test Ordered?

    If a doctor suspects a patient has one of the above-listed medical conditions, they may order this test. If a patient is experiencing the signs and symptoms associated with the above-listed disorders, this test may be ordered. Those signs and symptoms include fatigue, night sweats, weakness, enlarged spleen, weight loss, bleeding or bruising, frequent infections, paleness, joint and bone pain, paresthesia, headaches, visual distortion, dizziness, and itching.

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    How is this Test Done?

    This test is a blood test. The patient will sit and their hand or the crook of their arm will be used. A nurse or phlebotomist will use a butterfly needle (hand) or a venipuncture needle (crook of arm) to draw a sample of blood. This blood will then be sent to a lab for analysis. Once at the lab, a qualified scientist or doctor will look at the patient's blood under a microscope for specific antibodies and abnormalities. This test is performed on the granulocyte white blood cell genetic material.

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    What do the Results Mean?

    If a patient is experiencing the signs and symptoms of one of the above disorders, and a JAK2 V617F mutation is detected, it is highly likely they have one of those conditions, known as MPD. To confirm the diagnosis, the doctor will often perform a bone marrow biopsy. This biopsy will also help to determine how severe the disease is. If the test is negative, but the signs are there the doctor may still make a MPD diagnosis.

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    References

    Lab Tests Online. (2009). JAK2. Retrieved on October 25, 2009 from Website: http://www.labtestsonline.org/understanding/analytes/jak2/test.html