A patient with type A blood needs an emergency transfusion but no type A blood is available. Which blood type (A, AB, or O) can be safely given, and why?

What you are checking in an ABO transfusion

For red blood cell transfusions, you match the donor’s RBC antigens (A and/or B) against the recipient’s plasma antibodies (anti-A and/or anti-B). A dangerous reaction happens if the recipient has antibodies that bind to antigens on the donor RBCs.

What type A blood means

Type A blood has:

• A antigen on red blood cells
• Anti-B antibodies in the plasma

So, the key rule is: a type A recipient must not receive red blood cells that have the B antigen.

Testing each option (A, AB, O)

• Type A: Safe in general because it has A antigen only, but it is not available in this scenario.
• Type AB: Not safe because AB red blood cells have both A and B antigens. The recipient’s anti-B antibodies would bind to the B antigen, causing agglutination and hemolysis.
• Type O: Safe (as an ABO match) because type O red blood cells have no A or B antigens, so there is nothing for anti-B antibodies to attack.

One extra compatibility note

In real emergencies, the hospital also checks the Rh factor. If the patient is Rh negative, they should receive O negative blood when possible.