I don’t believe MPN’s can be “caught” from other people, and if they could be the folks handling blood donations would be screening for them.

That said, I donated blood regularly pre-diagnosis, and had been told for years after the pre-screening at the Red Cross that my Hgb and Hct ran a little high and could be indicative of a serious blood disorder.

I suspect my regular donations delayed the event (pulmonary embolisms) that led to my diagnosis.