A patient is brought in for a deceased-donor kidney transplant. Her PRA is Class I 45% and class II 60% by flow cytometry. Both her T and B cell crossmatch by the CDC technique are negative.
Should she receive this transplant? What is the difference between PRA and a crossmatch? What if you receive a report from the lab that while the crossmatch is negative, “DSA is present?”
The PRA gives the probability that a recipient will have anti-HLA antibodies against the variety of HLA antigens in a selected population. It is determined as part of the pre-transplant assessment when there is no particular donor identified. In contrast, the crossmatch test answers the question of whether a given recipient has anti-HLA antibodies against a particular donor, so-called “donor-specific antibodies” (DSA). A positive T-cell crossmatch, especially by the CDC technique, is associated with a very high risk of hyperacute rejection.
If the crossmatch test is negative, then this patient likely does not have high levels of DSA. Note that the crossmatch test can be done by both complement-dependent cytotoxicity (CDC) and the more sensitive flow cytometry method. This method may detect low levels of DSA that do not cause a positive CDC crossmatch.
Most centers will not transplant deceased-donor organs into a patient with a positive CDC crossmatch. The approach to a positive flow crossmatch or DSA alone varies. Some transplant centers will avoid transplantation while others may use more intensive immunosuppression at the time of transplant. In the case of a living donor, “desensitization protocols” may be used pre-transplant when the crossmatch is positive or DSA is present.
PRA and cross-match do not relevantly affect outcome after liver transplantation and are therefore not routinely performed pre-liver transplant.