Hmm. A bone marrow biopsy is usually the gold standard for ET diagnosis. I wonder if asking these questions would help:

Do I have essential thrombocytosis?

If the answer is yes, ask: What are the treatment goals and what will you try if the hydroxyurea doesn't work?

If the answer is no or I don't know, ask: Would consulting with another hematologist be of help?

I have found that asking questions where the doc has to give you yes/no/I don't know answers prevents them from giving you a bunch of doc-speak answers that leave you confused about what's going on.

Do you have someone going with you to the doctor who can take notes? Sometimes that helps.

If you have a GP, I'd say that telling him or her that you are not getting answers from the hemo and want a secondary referral would be one way you could go.