*Purpose: Utilizing non-A1 donors for O or B recipients with low anti-A titers presents an opportunity to expand living donor kidney transplantation. Since February 2018, the National Kidney Registry (NKR) performed confirmatory subtyping on all blood type A living kidney donors entered into the registry for paired kidney exchange. This was done regardless of local program protocol or results. If the subtype through NKR was non-A1, confirmatory molecular typing was completed.

*Methods: We reviewed NKR subtyping data from 2/1/2018 to 10/1/2019 and compared the results with the local subtyping from participating transplant centers.

*Results: Over the study period, 492 blood type A donors were entered into the NKR registry. 51 of the 492 (10.4%) donors were serologically subtyped as non-A1 and molecularly typed as A2 by the NKR. 32 of those 51 (62.7%) were initially subtyped serologically as A1 by the local transplant center. The remaining 19 of 51 donors (37.3%) were successfully registered as A2 kidneys, since the transplant center had subtyped them serologically as non-A1. Although most AB samples were not subtyped for A locally, two donors who were subtyped serologically by the local transplant center as A1B were found by the NKR to be non-A1B serologically and A2B by molecular typing.

*Conclusions: We observed a high rate of discordant A subtyping (62.7%), and in the majority of cases the NKR could not correct the typing under current United Network of Organ Sharing (UNOS) policy. UNOS allocation policy prohibits the use of blood type A donors with discrepant or indeterminate subtyping to be allocated as A2 donor kidneys. Most of the kidneys subtyped by the NKR as A2 were transplanted as A1 kidneys, representing a lost opportunity for optimal use of these organs. We discuss various approaches that might allow programs to overcome barriers for optimal utilization of non-A1 donors.

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