@rabab101, I found this information and negative or non-detectable JAK2
"Negative results for all JAK2 mutations does not necessarily rule out an MPN—the person may have a JAK2-negative MPN or the JAK2 mutation was not detected during testing. The JAK2 tests are performed on the genetic material found in white blood cells called granulocytes (from blood or bone marrow) and red cell precursors (from bone marrow). Not all granulocytes and red cell precursors will possess the JAK2 mutations. The proportion of affected cells will vary from person to person and may change over time. If there is only a small number of cells that have the mutation in the blood sample tested, then it is possible that the mutation will not be detected." You can read more here:
- JAK2 Mutation Test https://www.testing.com/tests/jak2-mutation/#:~:text=The%20JAK2%20V617F%20test%20may,results%20associated%20with%20these%20MPNs.

What further testing is your brother scheduled for to confirm or rule out polycythemia vera?