"Red-blooded" means: 1) A person, full of energy, strength and is having great bodily or mental health. 2) Someone, who is sexually active. 3) A person, who behaves in a traditional way, which is considered typical of a particular kind of person. For example, 1) Jack looked at that girl, as any red-blooded {meaning 2} youngster would do. 2) I think that John Cena is a true red-blooded {meaning 1} full wrestler, who always performed with vigor and aplomb.

Because 'Red-Blood' is not a meaningful phrase, at least, to me. So, I just added 'ED' after 'blood' to make it meaningful. And now, 'Red-Blooded' is a meaningful phrase, which I explained. But 'Red Blood Cells' makes sense, or any other phrase like that.

Why did you explain 'red blooded' without the poster saying that 'red blooded' is the phrase he intended to use?

The correct phrase is "Red Blooded" not "Red Blood". But "Red Blooded American" is, certainly, a phrase, but I explained "Red Blooded" here.

Can you use it in a context? Where did you see the phrase? The most common example I know of is "A red blooded American" but your context might be different.