Question

why is it important to know a persons rhesus factor before a blood transfusion?
a patient who is rh+ can receive only rh− blood.
a patient who is rh− can receive only rh+ blood.
a patient who is rh+ can receive only rh+ blood.
a patient who is rh− can receive only rh− blood.

Explanation:

The rhesus (Rh) factor is an antigen on red - blood cells. A person with Rh - negative blood has antibodies against Rh - positive blood if exposed to it. So, an Rh - negative patient can only receive Rh - negative blood to avoid an immune reaction. An Rh - positive patient can receive both Rh - positive and Rh - negative blood.

Answer:

A patient who is Rh− can receive only Rh− blood.