Platelets in "normal people" fluctuate a lot. So do ours, just at higher-than-normal levels. In my own experience before going on HU, drops and spikes could be as much as 100 points. Docs are looking at cumulative upward trend, which can be gradual or steep in ET. Your drop might indicate that your trend might be more gradual.

A good question to ask your doc at next visit is how he makes the decision to start platelet reduction therapy.

FWIW, I've been on HU for 6 years, and my lowest reading was 423 and my highest 537, with all other blood counts normal. My hemo calls that "very stable."

How are you feeling?