Final answer:
In the absence of B negative blood for transfusion, the preferred alternative for a B negative blood type patient is O negative blood, as it is the universal donor type and lacks both A and B antigens, as well as the Rh factor.
Step-by-step explanation:
In the case where a B negative blood type client requires a transfusion and the same type is not available, the universal donor blood type, which is O negative blood, should be used. Blood type B negative lacks both A antigens and Rh antigens on the surface of erythrocytes. Thus, there are no antigens to react with the antibodies in the O negative donor blood.
The transfusion of O negative blood is deemed safe because the red blood cells contain neither A nor B antigens, which could provoke a response from the recipient's anti-A or anti-B antibodies, and they are Rh negative, which means they do not contain the Rh antigen that could provoke a response from any potential anti-Rh antibodies in a Rh negative recipient. Therefore, in situations where a perfectly matched blood type is not available, O negative is preferred for individuals with B negative blood.