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
antibodies, which would bind with the
blood, causing a hemolytic reaction and possible systemic damage.
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).