What would be the most likely outcome for a patient who has previously been transfused with Group O blood?

The most likely outcome for a patient who has previously been transfused with Group O blood is the detection of unexpected antibodies.

Group O blood lacks both A and B antigens on the surface of red blood cells, which makes it compatible with any ABO blood group for transfusion. However, individuals with Group O blood typically have antibodies against both A and B antigens (anti-A and anti-B) present in their plasma. If a patient with another blood group receives Group O blood, their immune system may recognize the A and/or B antigens from other transfusions or exposures as foreign, leading to the formation of unexpected antibodies against these antigens.

Consequently, in the context of a blood transfusion, the presence of unexpected antibodies could pose a safety risk for future transfusions, particularly if there is a need for red cell transfusions in which recipients could develop hemolytic reactions if not adequately matched.

The other options do not accurately represent the typical immunological response of a patient transfused with Group O blood, as the presence of anti-A or anti-B antibodies would be expected only in non-O blood group patients, while the absence of antibodies is unlikely due to the transfusion history. Thus, unexpected antibodies would be the most relevant outcome to