If a patient had a hemoglobin level in the 40s (4s) how poss is it they could die given its not sudden bloodloss & theres no other serious med issues?

Can you explain?: It sounds as if someone close to you died unexpectedly and was known not to be anemic. There are many other causes of death. If you are next-of-kin, you have the right to get an explanation from the physician in charge. Otherwise, ask the family for the actual cause as given, and consider asking for an autopsy if it's not clear.