My doctor for the trial told me it can be caused by a high platelet count. Sure enough when that went down so did my potassium level. I don't think my primary realized there was a correlation.

Thank you Janet. I thought there was a correlation.

Hi, I’ve had high platelets, ET but now somewhere between ET and MF for sixteen years. Just this past year….I have had high potassium counts. If I reduce the high potassium foods from my diet the level goes back within the normal range. I mention this to the PA I see for the clinical trial I’m on as well as to my MPN specialist, and they both say it can result with ET. And has something to do with the high number of platelets sitting in the tube of blood….some reaction. But, I’ve looked at CMPs way back to 2007 onward and I never had a high reading until this year.

Since I originally posted this question I have learned a high platelet count can coincide with high potassium

Many of us use a "lite" salt so as to not get too much sodium. The "lite" has potassium instead of sodium. Stopping the use of "lite" salt reduced my wife's potassium back down below maximum range. She does have Jak2 but had thrombocytosis which is controlled with Jakafi.