I'm happy to share my experience. #1. No, do not need to give blood. The Hydrea is toxic enough to kill the excess platelets. #2. I have experimented over the years to cut back a little from the prescribed dosage simply to minimize the amount of toxicity I'm consuming. My Docs have not liked this kind of fooling around with the dosage. So I've been steady at 6 days a week, no Sundays for about a year. No side effects from the Hydrea after the initial first month twenty years ago. #3. I still have no symptoms of this strange blood disorder called ET, regardless what my count is on any given day. I go every 3 months for a cbc. It puzzles me that at 72, I still feel the same with a count of 480 as I did at age 40 when I was diagnosed with a count of 800. #4. My two Docs (first one retired) have dangled the ultimate fear over me since the diagnosis, but so far my ET has not morphed into leukemia. Having no symptoms and in disbelief, I went to the Scottsdale Mayo Clinic for a second opinion at some point in the 1990s. Same diagnosis. Very disappointing because I was really convinced that nothing was wrong with me. Thanks for sharing the NIH info. I always like to run across updated information on PV,ET, and other blood disorders. You may never progress to anything more advanced. Best wishes.