blood groups

[kapilkumar.g]

why "o"group is called universal doner

[bednobs]

Putting aside positive and negative for the moment -

because they can give blood that anyone could recieve
If you didnt know someones blood group but needed to give them a transfusion you could give them "O"

Alternatively, the "universal recipient" is AB because they could recieve either a, b, o or ab blood and suffer no ill effects

[whiffey]

Note that group O whole blood (in the plasma) contains naturally-occuring antibodies to A, B, and AB cells, therefore in theory at least, transfusing large amounts of group O whole blood is not a good idea. However, whole blood is not used (ever?) nowadays, rather blood components such as packed red cells, fresh frozen plasma, etc.