Determination of unacceptable human leukocyte antigen (HLA) mismatches (UAM) before kidney transplantation (KT) aims at minimizing immunological risk and routinely involves Luminex single antigen bead (SAB) testing. SAB-UAM criteria, however, often lack standardization. We implemented standardized mean fluorescence intensity (MFI)-based SAB-UAM criteria in four German transplant centers and prospectively studied the consequences on waitlist composition as well as waiting time, early antibody-mediated rejection (AMR) and graft loss in 267 patients. HLA were deemed unacceptable in case of CDC-reactivity or antibodies against known HLA from previous transplants irrespective of MFI. For all other antibodies, the MFI cut-off was 5.000 with the exception of 10.000 for anti-HLA DQ. We observed significant accumulation of highly sensitized patients (virtual panel-reactivity >95%) on the waiting list during the study period. Median time to KT was longer in patients with UAM, but differences were not statistically significant. Patients with preformed donor-specific anti-HLA antibodies (DSA) below the UAM cut-off criteria (39/267) experienced more AMR episodes compared to DSA-negative patients (10.3% vs. 1.3%, p < 0.001). Graft survival, however, was not statistically different over a median follow-up of four years. Standardized SAB-UAM criteria associated with good short-term outcomes but resulted in accumulation of highly sensitized patients on the waiting list.