If his blood type is "AB" (either "+" or "-") he is a "universal recipient" and is compatible to receive a kidney from a person of ANY blood type (O, A, B, AB) either "+" or "-". It might be wise to mention this in your postings, as there are many people who mistakenly think that blood types must be identical for kidney transplants. You can confirm this information with the transplant coordinator or doctor.
best wishes,
Fr. Pat