Blood-tests Explained


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This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

JAK2 Mutation


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 healthcare 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

The Test Sample

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.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test