I take Hydroxyurea for PV. My platelets vary monthly! Anywhere from 390to almost 500. I’m 58 and for now my doctor said under 600 is acceptable for me. I don’t have any other health issues thus far and I’m sure that’s a consideration. If they do go higher he said all we do is up dosage. I currently am doing well 3X a week and hope to stay that way hehe Try not to worry. I don’t think anyone’s platelets stay the same when doing monthly labs.