Quote Originally Posted by Noblejanobii View Post
So here's how it works. Generally speaking negative blood types are rarer than positive blood types. Positives can accept negative blood donations within their own blood type, ie A positive can receive A negative, but cannot receive B negative. Negatives, however, can only take their own blood type, which is one of the reasons O negatives are needed so badly is because O negative can only take O negative. O negative is also the universal donor which is why the blood packs they keep in ambulances are always O negatives, because anyone can take it.

Rarity wise, AB blood types are the rarest, with AB negative being the rarest blood type. AB positive is the second rarest, B negative is third, A negative is fourth, O negative is fifth, and B positive is sixth with all them (at least in Caucasians) being below 10% in regards to how many people have them. The only two above 10% in Caucasians are A+ and O+ because of how the genetics work.

So as I said before O negative is the universal donor, but that's generally only for red blood cells. For plasma donations, it's AB (doesn't matter if it's positive or negative). In addition, the universal receiver is AB positive because it can take donations from all forms of blood. AB negative technically falls into this category as well but since it can't take AB positive blood, it somewhat falls short.

Oddly enough in my family I have some of the rarest blood types, with my grandfather on my dad's side being AB+, my grandma on my dad's side, my mother, my aunt, and I all being O-, and my father is a B+.
Ive read about even more rare blood types that dont ever get mentioned. It was cool finding out that there could be more.