Must one spit to confirm the presence of blood in the mouth while fasting, and is it sufficient to expel the blood without rinsing the mouth during a Ramadan day?

Intentionally swallowing blood that has come out of the mouth is impermissible and invalidates the fast. It must be expelled. If a fasting person intentionally swallows it, their fast is invalidated. If it precedes them unintentionally, their fast is valid. There is no need to confirm the presence of blood unless it is genuinely felt. If it is found and expelled, then rinsing the mouth afterwards is advisable so that the fast is not invalidated by saliva mixed with blood or its trace, unless the blood is profuse and difficult to guard against, in which case its trace is excused, and expelling it is sufficient.