Well, hemoglobin is a very narrow term, even blood is a restrictive keyword. So if I work in the medical field I would want a name that does not limit my scope of operation. Something with a broader purpose. I don't think blood tests are limited to testing for hemoglobin.
Plus, domain hacks are unprofessional imo.
Just because it is a generic keyword doesn't mean it has a practical purpose, or that somebody would want to buy it from you. That's why it was unregistered.
BTW isn't the correct spelling hemoglobin ?