@jodyjazz Starting HU depends on 3 things: Driver mutation, age, and clot history. Some young folks who have never had a clot and are CALR+ are started when platelets are 1,000. Patients over 60 with JAK2 and a clot go might go on HU at 500.

Everybody goes on aspirin, because that's the best preventive for clots. And no clots, no HU, at least for awhile
Patients who cannot take aspirin often take a substitute blood thinner.

I am CALR+. At 64, I was started on 500 mg of HU daily when my platelets started creeping up to 800 pretty fast. I've never had a clot, but if platelets go over 1,000 the docs start worrying about your developing von Willebrand's Syndrome, which can cause bleeding.