What is the primary purpose of performing a donor-recipient crossmatch before transplantation?

• A. To determine matching blood type
• B. To detect preformed donor-specific antibodies in the recipient
• C. To assess kidney function
• D. To determine antigen presentation ability

Answer: (B)

The main idea is to detect preformed donor-specific antibodies in the recipient that could attack the donor’s antigens, especially HLA, after transplantation. The crossmatch tests the recipient’s serum against donor lymphocytes; if antibodies in the serum bind the donor cells and activate complement, you get a cytotoxic or fluorescent reaction. A positive crossmatch signals a high risk of immediate, antibody-mediated graft injury (hyperacute rejection), so the transplant may be postponed, the donor changed, or desensitization considered. A negative crossmatch suggests no detectable donor-specific antibodies, meaning the graft is less likely to face this immediate immune attack.

ABO compatibility is still necessary, but the crossmatch specifically evaluates whether the recipient has antibodies against the donor’s HLA antigens. It isn’t about kidney function, nor about the recipient’s general ability to present antigens.