An AB- patient needs a blood transfusion but AB- is unavailable. What is an acceptable alternative blood type for transfusion?

For a patient with AB- blood type, the safest alternative for a blood transfusion is A-. This is because AB- individuals can receive blood from AB-, A-, B-, and O- blood types. The key factor here is the Rh factor; AB- can tolerate blood from Rh-negative types without the risk of an immune reaction.

A- blood is Rh-negative, allowing it to be safely transfused into an AB- patient. The compatibility of ABO blood groups means that A- can be accepted without introducing the corresponding antibodies that could lead to a transfusion reaction.

In contrast, options such as A+ or B+ introduce Rh-positive blood into an Rh-negative patient, which could provoke an immune response. Similarly, O- is also a compatible type, but since A- is listed as an option and also compatible, it is the correct choice that fits within the parameters of the question.