What happen when you inject someone with a different blood group to theirs..?

Question

so when doctors ask for blood donors it has to be the same blood group..

what if its the wrong group..what happens?

is it dangerous?

Answer 1

The A and B part of the A/B/O designation refer to sugars that are attached to the outside of red blood cells and act as "antigens"--they can be recognized by an immune system and attacked if they are different from "self."  So if you are type A, your own immune system will not attack other type A blood but will attack anything with a B antigen (B or AB blood).

Type O indicates the absence of either of those antigens, so there's nothing to attack and that's why type O is called the "universal donor."  Type AB, conversely, won't react to either antigen because both are part of their natural system, so they are "universal recipients."  (But they can donate blood only to other type ABs.)

There are actually a whole host of other things in donor blood that could potentially be reactive, so in reality you can always have a transfusion reaction, but for textbook purposes they usually just look at A/B/O and Rh factor (that's the thing that they list as 'positive' or 'negative').  Plasma, platelets and other constituents of blood are not considered to be immunologically active--you can generally give platelets from any blood type to any other blood type, for example, as long as they don't also contain red blood cells.

Transfusion reactions can be very dangerous indeed, even fatal.  When the body attacks the foreign red blood cells, they split open ("hemolyze") and spill their contents into the bloodstream--some of the constituents are very bad for you in large amounts.  Plus, of course, if the RBCs are being destroyed, they can't do the job that they were given for, which is to carry oxygen to the whole body.  No oxygen delivery is bad too.

The most common complication of a transfusion is a fever (or, in medspeak, a "febrile non-hemolytic transfusion reaction").  All you really do for that is to stop the transfusion.  *g*

Answer 2

Yes.  The only blood that can be used for all purposes is O. A, B, & AB (either possitive or negative) are dangerous to other bloodgroups.  But lately they split blood, into platelets, white bloodcells, red bloodcells, plasma etc.  Don't know what the effect of those are.

Peace.