Final answer:
Before donating blood, a cross-matching test is conducted to determine the blood type and ensure compatibility with the recipient.
Step-by-step explanation:
Before someone donates blood, a cross-matching test is done first to determine their blood type. This test involves mixing the donor's blood with commercially prepared antibodies against the A, B, and Rh antigens. By confirming the blood type and ensuring compatibility between the donor and recipient, the risk of a transfusion reaction is minimized.