Details

A blood donation is medically safe if both the groups and the Rh factors are compatible. Group compatibility is actually more restrictive than Rh factor compatibility. In fact, when the group rules are not followed, a hemolytic transfusion reaction (rupture of red blood cells) can take place, possibly resulting in a fatal response. When considering the Rh factor, the only restriction () could be bypassed in an emergency situation, provided that the recipient has not been exposed to the antigen in a previous transfusion or a previous pregnancy (in an woman with an child). Such previous exposure would produce, in the recipient, antibodies, which would bind with the blood, causing a hemolytic reaction and possible systemic damage.

Snapshot 1: donation is permissible for both the groups and the Rh factors

Snapshot 2: donation is forbidden because of incompatible groups

Snapshot 3: donation is forbidden because of incompatible Rh factors

Snapshot 4: the donation chart shows that the group can be considered as the universal donor (first, fully green column on the left) and the group can be considered as the universal recipient (bottom, fully green row).

Reference

[1] I. Asimov, The Bloodstream: River of Life, New York: Collier Books, 1961.