A 40-year-old patient with end-stage renal disease is being evaluated for a kidney transplant. To prevent hyperacute rejection, which of the following pre-transplant tests is most critical?

Explanation

Hyperacute rejection is primarily mediated by pre-formed antibodies in the recipient against donor antigens. The lymphocyte cross-match test directly detects these pre-formed antibodies (e.g., anti-HLA antibodies) in the recipient's serum that react with donor lymphocytes. A positive cross-match is a contraindication to transplantation due to a very high risk of hyperacute rejection. While ABO compatibility (B) is also crucial to prevent hyperacute rejection due to anti-ABO antibodies, the cross-match specifically addresses anti-HLA antibodies, which are a major cause of hyperacute rejection in ABO-compatible settings. HLA typing (A) is important for minimizing acute and chronic rejection but doesn't directly detect pre-formed antibodies. PRA screening (D) identifies the presence and breadth of anti-HLA antibodies in the recipient's serum, indicating sensitization, but the cross-match is the definitive test for donor-specific antibodies immediately prior to transplant.