*Purpose: The use of ABO incompatible (ABOi) living donors is an attractive solution for expanding the liver donor pool. We investigated the impact of the baseline anti-A/B IgG titer on the transplant outcomes in ABOi liver transplantation (LT).

*Methods: We analyzed 394 adult patients who underwent living donor LT (303 ABO compatible LT and 91 ABOi LT) between 2012 and 2018. ABOi LT patients were categorized by baseline IgG titer: low IgG titer (≤ 1:64, n=51) versus high IgG titer (≥ 1:128, n=40). All ABOi LT patients received desensitization therapy including rituximab and plasmapheresis.

*Results: Patients with high IgG titer experienced antibody rebound (≥ 1:64) more frequently than those with low IgG titer during the first month after LT (35.0% vs. 15.7%, P=0.033). Patient survival rates for ABO compatible, low IgG titer, and high IgG titer were 85.0%, 91.5%, and 74.4%, respectively, at 3 years post-transplantation (P=0.006). High IgG titer (HR, 2.76; 95% CI, 1.39-5.48; P=0.004) and MELD score of >20 (HR, 2.32; 95% CI, 1.22-4.41; P=0.010) were independent risk factors for mortality. Infection was the leading causes of death in all groups, but the proportion was significantly higher in high IgG titer group than in other groups (81.8% vs. 30.8% vs. 33.3%).

*Conclusions: Patients with high IgG titer (≥ 1:128) are associated with a higher risk of death after ABOi LT than those with low IgG titer (≤ 1:64). Thus, ABOi LT patients with high IgG titer should be managed with great care.

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