Does virtual crossmatching eliminate the need for physical tests entirely?

Virtual crossmatching does not eliminate the need for physical tests. Instead, it is a strategy used to predict the outcome of a physical crossmatch and improve organ allocation efficiency. Physical crossmatch tests remain the final step to confirm compatibility before surgery. Unlike the virtual crossmatch, which relies on computerbased antibody and HLA data, physical tests use real donor and recipient samples to observe immune reactions directly.

The process follows these steps:

• Sample Testing: After the computer algorithm identifies a potential match, the transplant center arranges laboratory testing for both donor and recipient.

• Specific Assays: Tests such as ComplementDependent Cytotoxicity (CDC) and flow cytometry crossmatch are performed. These assays mix the recipient’s serum with donor cells to determine whether the recipient’s antibodies bind to donor tissue.

• Final Approval: The results of these physical tests guide the transplant team in making the final decision about surgery, ensuring that the risk of immediate rejection is minimized.

This twostep approach—first virtual, then physical—is essential because antibody levels can change over time, and physical tests may detect risks that computerbased evaluations cannot.

Key reasons why physical tests and further verification remain necessary include:

• Predictive Nature: The virtual crossmatch is designed to predict a negative crossmatch based on unacceptable antigens. It is not a definitive biological confirmation.

• Clinical Contraindications: A positive CDC crossmatch remains a clinical contraindication for transplantation.

• Assay Limitations: Solidphase assays (such as Luminex) used in virtual crossmatching have technical limitations. They may produce false positives due to neoepitopes formed during recombinant antigen production, or false negatives due to seruminterfering substances or antibody spreading across multiple antigens.

• NonHLA Antibodies: Although solidphase assays are the most practical method for detecting nonHLA antibodies, their detection remains challenging. Surrogate endothelial cells used as sensors do not always express antigens such as MICA consistently.