Paired Exchange Program for Incompatible Couples: Why Might a Potential Donor Be Incompatible With You?
A donor is considered incompatible when medical tests show that the recipient’s immune system would likely reject their kidney. This is a common barrier for friends or family members who want to donate but cannot proceed with a direct transplant.
Two major medical reasons explain donor–recipient incompatibility:
- ABO Blood Group Incompatibility
The most frequent cause of incompatibility is a mismatch in blood type. Successful transplantation requires compatible ABO blood groups. For example, a donor with blood type A cannot donate to a recipient with blood type B, and vice versa.
Some combinations are especially challenging:
- Patients with blood group O have the fewest compatible donors.
- AB donors are rarely compatible with recipients of other blood types.
- These groups often face longer waiting times or require paired exchange programs.
- HLA Incompatibility and Donor-Specific Antibodies (DSA)
Even when blood types match, incompatibility may still occur due to differences in HLA tissue type. This happens when the recipient has pre-formed HLA antibodies—also called donor-specific antibodies (DSA)—that recognize and attack the donor’s tissue.
These antibodies can:
- Trigger immediate or early rejection
- Increase the risk of graft failure
- Lead to a positive crossmatch test, which indicates immunological incompatibility
When a positive crossmatch is present, a direct transplant is unsafe, and the pair may be referred to a paired exchange program to find a compatible match.
