*Purpose: ABO incompatible (ABOi) kidney transplantation (KT) has been considered to overcome donor shortage. We investigated the long-term clinical outcomes in ABOi KT in patients with high baseline anti-A/B antibody titer.

*Methods: We retrospectively included 260 patients who had undergone ABOi KT from May, 2009 to November, 2020. One hundred and eighty-one patients with a baseline immunoglobulin G (IgG) titer of ≥1:128 were assigned to the high-titer group and 79 patients with a baseline titer of ≤1:64 were assigned to the low-titer group. We used a protocol composed of rituximab, plasmapheresis, and intravenous immunoglobulin (RTX/PP/IVIG). We compared the clinical outcomes of the two groups.

*Results: The median follow-up periods were 56.57 months (high-titer group) and 38.77 months (low-titer group) (p = 0.003). The high-titer group required more sessions of PP/IVIG than the low titer group (7.75±3.10, 3.59±1.91, p < 0.001, respectively). Patient survival at 5 years was 93.50% in high-titer and 96.70% in low-titer group (p = 0.689). Graft survival at 5 years was 87.20% in high-titer and 95.80% in low-titer group (p = 0.922). During the follow-up period to one year, antibody titer remained higher in the high-titer group. And serum creatinine showed no difference between two groups up to 6 years (p for interaction = 0.730). No significant differences were detected in the graft survival rate, patient survival rate and rejection-free survival rate between two groups. However, the infection-free survival rate was significantly lower in the high-titer group (p = 0.032). The incidence of bacterial infection was higher in high-titer group (46.84% vs. 27.07%, p = 0.002).

*Conclusions: Patients with high baseline anti-A/B IgG isoagglutinin titers had equally successful long-term outcomes as those with low titers. However, ABOi KT in the high-titer group may require greater caution compared to the low-titer group because of the higher tendency of infection.

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