*Purpose: Obesity is emerging as important health problems worldwide. In recent years, with the development of desensitization therapy, successful kidney transplantation has been performed even in sensitized patients. Previous studies have examined the relationship between recipient obesity and graft loss rate, which has been reported that graft loss rate increases as body mass index (BMI) increases. However, there is no research on the effect of graft loss on high BMI in pretransplant sensitized patients. Therefore, the aim of this study is to investigate the relationship between obesity and pretransplant sensitization status.

*Methods: This study was retrospective, observational, and single center design. From January 2010 to December 2018, patients who underwent ABO matched living donor kidney transplantation at Seoul St. Mary’s Hospital were enrolled. BMI was calculated on the basis of height and weight at the time of transplantation and defined as obesity group when BMI was above 25. Pre-sensitized group was defined when the median fluorescence intensity of pre-transplant donor specific anti-HLA antibody was higher than 5000. The primary outcome was the death-censored graft loss rate and the secondary outcomes were the overall graft loss rate, patient mortality rate, and biopsy-proven acute rejection rate.

*Results: Of total 682 patients, 499 patients were normal weight group and 183 patients were obesity group. And 638 patients were non pre-sensitized group and 44 patients were pre-sensitized group. The odds ratio of death-censored graft loss of obesity itself was 1.835 (0.989-3.405) with marginally statistical significance (P=0.051), and the odds ratio of overall graft loss was 1.664 (1.002-2.764). However, there was no significant difference in acute rejection rate and patient mortality rate according to obesity status. And the odds ratio of acute rejection of the pre-sensitized itself was 5.180 (2.771-9.685), but there was no significant difference in death-censored graft loss rate, overall graft loss rate, and patient mortality rate. The Cox proportional hazard ratio (HR) of obesity for death-censored graft loss was 1.931 (1.068-3.492), and the HR of pre-sensitization was 2.079 (0.821-5.264). However, when we integrated the obesity and pre-sensitization, HR was much increased to 8.052 (1.930-33.600).

*Conclusions: Living donor kidney transplantation recipients who were pre-sensitized and whose BMI were above 25 have a greater risk of allograft loss than those who do not. Our results suggest that pre-sensitizatization and obesity may have a synergistic adverse impact on long-term post-transplant allograft survivals.

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