What is considered an absolute contraindication to kidney transplantation?

In the context of kidney transplantation, an absolute contraindication is a clear condition or situation that completely prevents the procedure from taking place due to the significant risk it poses to the recipient. A positive NIH T cell crossmatch is indeed considered an absolute contraindication to kidney transplantation.

When a T cell crossmatch is positive, it indicates that the recipient has pre-existing T cell sensitization against the donor's major histocompatibility complex (MHC) antigens, which can lead to acute rejection of the transplanted organ. This sensitization suggests that the recipient's immune system is likely to mount a robust response against the transplanted kidney, severely jeopardizing the success of the transplant and the health of the recipient.

In contrast, while a positive B cell crossmatch and a positive AHG-augmented T cell crossmatch indicate a level of sensitization, they may not at all times universally preclude kidney transplantation depending on the clinical scenario and available treatments. The consideration of crossmatching results often involves careful assessment by the transplant team regarding the overall risks and benefits of proceeding with the transplant. The pairing of A2 blood group donors with O recipients is typically a strategy employed to increase donor options and would not be classified as an absolute contraindication either.