To help diagnose myeloproliferative disorders (MPDs)
JAK2
JAK2
Também conhecido como
Janus Kinase 2
Nome formal
JAK2 V617F; JAK2 exon 12 and 13
Este artigo foi revisto pela última vez em
Este artigo foi modificado pela última vez em 10 de Julho de 2017.
At a Glance
Why Get Tested?
When To Get Tested?
When your doctor suspects that you may have polycythemia vera, essential thrombocythemia, or primary myelofibrosis
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is it used?The JAK2 V617F test may be used, along with other tests such as erythropoietin, to help diagnose the myeloproliferative disorders (MPDs) polycythemia vera (PV), essential thrombocythemia (ET), and agnogenic myeloid metaplasia (primary myelofibrosis, PMF). It may be ordered as a follow-up test if a person has an increased hemoglobin and/or platelet count and the doctor suspects that the person may have an MPD.
The JAK2 exon 12 and JAK2 exon 13 tests may be ordered to help diagnose PV cases that are negative for the JAK2 V617F mutation.
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When is it ordered?The JAK2 V617F test may be ordered along with other tests when a doctor suspects that a person has PV, ET, or PMF because routine laboratory results such as a CBC reveal abnormal results associated with these MPDs and/or because the person has signs and symptoms that suggest an MPD.
Sometimes MPDs may have no symptoms or a few, relatively mild symptoms and may be present for years before being diagnosed, often during a routine physical. However, if certain signs and symptoms appear, a doctor may suspect that the patient has one of these MPDs. They have many signs and symptoms in common, for example:
- Weakness and fatigue
- Weight loss
- Enlarged spleen (splenomegaly)
- Bleeding and bruising, due to low and/or abnormal platelets
- Night sweats
- Bone and joint pain
- A pale appearance due to anemia (when red blood cells are decreased)
- Frequent infections
PV may also be suspected when symptoms such as headaches, dizziness, visual distortion, itching and paresthesia appear. In PV, there is an excess number of red blood cells and this may lead to complications, such as stomach ulcers, kidney stones, venous thrombosis, stroke, and rarely to congestive heart failure.
Those with ET usually have no symptoms, but some may develop inappropriate blood clots (thrombosis) or bleeding (hemorrhage) because there are increased numbers of platelets produced that do not function properly. This may cause symptoms in addition to those listed above such as tingling in the hands and feet, headaches, dizziness, nosebleeds, and easy bruising.
About one third of patients with PMF have no symptoms. People who do have symptoms may have those that are associated with anemia such as fatigue and weakness. A JAK2 test may be done if routine laboratory tests suggest PMF.
The JAK2 exon 12 and JAK2 exon 13 tests may be ordered when the JAK2 V617F test is negative and the doctor suspects PV.
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What does the test result mean?If the JAK2 V617F mutation is detected and the person has other supporting clinical signs, then it is likely that he has a MPD. Other testing, such as a bone marrow biopsy, may need to be performed to determine which MPD the person has and to evaluate its severity.
If the JAK2 V617F test is negative but a JAK2 exon 12 or exon 13 mutation is detected and the person has supporting clinical signs, then it is likely that the person has PV.
If the person is negative for all JAK2 mutations, they may still have an MPD. They could have a JAK2-negative MPD or their JAK2 mutation was not detected during testing. The JAK2 tests are performed on the genetic material found in granulocyte white blood cells, but not all granulocytes will contain the JAK2 mutations. The proportion of affected cells will vary from person to person and may change over time. If there is only small number in the blood sample tested, then it is possible that the mutation will not be detected.
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Is there anything else I should know?A few laboratories are offering both qualitative and quantitative JAK2 V617F tests. Some doctors may order a quantitative test to monitor the change in the number of cells with the JAK2 V617F mutation over time. Currently, the quantitative test is not performed frequently and its clinical utility has yet to be strongly established. If future research shows that the JAK2 gene is an appropriate target for MPD therapies, then it is possible that the quantitative test may be ordered periodically to monitor the effectiveness of treatment. There is still much to be learned about MPDs and about how, and if, the JAK2 mutations contribute to the progression and prognosis of MPDs.
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Can this test be done in my doctor's office?JAK2 mutation testing must be performed in a laboratory that performs molecular testing. It is not offered by every laboratory and must often be sent out to a reference laboratory.
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Should everyone have a JAK2 V617F test performed?
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Is there any reason to repeat a JAK2 V617F test?A doctor may repeat this test if it was negative and she feels that the mutation may have been missed. One reason it might be negative is that the proportion of your cells that have the JAK2 V617F mutation may be low. Currently, the test is not nationally standardized, so the sensitivity of the test may vary somewhat from laboratory to laboratory. A second test done at a later time and/or sent to a different laboratory may detect the JAK2 V617F mutation if it is present.
Also, some doctors may order a quantitative test periodically to monitor the change in the number of cells with the JAK2 V617F mutation over time. Results from repeated quantitative tests may be useful in monitoring the effectiveness of treatment if ongoing research shows that the JAK2 gene is an appropriate target for MPD therapies.
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Are there other genetic tests associated with MPDs?Yes, mutations in the myeloproliferative leukemia gene (MPL) have been associated with ET and PMF, but not with PV. Genetic testing is also sometimes used to check for the presence or absence of a Philadelphia (Ph') chromosome or a bcr-abl translocation in a person suspected of having the MPD CML (chronic myelogenous leukemia).