*Purpose: The impact of pre-transplant (pre-TXP) bariatric surgery (BS) on outcomes after liver transplant (LTX) has not been completely elucidated. Roux-en Y gastric bypass (RYGB) is a common BS procedure. Primary objective: to identify the risk of infection in LTX recipients with pre-TXP RYGB; specifically, rates of bacterial infection, fungal infection and CMV. Secondary objective: evaluate transplant outcomes (rejection, graft and patient survival)

*Methods: Adult patients receiving a LTX between 1/1/2001-9/30/2018 at our center were included. This population was then screened for pre-TXP RYGB. Patients with gastrectomy via sleeve or banding were excluded. Patients without a history of BS including gastrectomy pre or post-transplant were placed in a comparator group, matched 2:1 on transplant vintage and age.

*Results: There were 16 LTX recipients with pre-TXP RYGB matched to 32 controls. Median time from RYGB to transplant was 11.7 years. Mean weight loss attributed to RYGB in those with data available was 66 ± 19 kg. There were significantly more women with pre-TXP RYGB than in the matched control (RYGB: 68.8% vs control: 25% p=0.009). Demographics were otherwise similar between groups including rates of donor/recipient CMV seropositivity. There was no difference in use of induction or maintenance immunosuppression. History of pre-TXP RYGB did not significantly increase hospital or ICU length of stay (p=0.5, p=0.3) in our cohort. However, pre-TXP RYGB was associated with a significantly increased rate of fungal infection at 1 year (RYGB: 33.4% vs control: 9.7%, p=0.01), and a numerical trend to increased bacterial infection (RYGB: 56.2% vs control: 32.2%, p=0.09). Rates of CMV were not significantly different at 1 year (RYGB: 26.7% vs control 12.9%, p=0.3). Pre-TXP RYGB was not associated with increased rejection rates (RYGB: 6.7% vs control: 16.1%, p 0.78) or reduced patient survival (RYGB: 93.8% vs control: 96.9%, p 0.17) at 1 year. However, there was a numerical trend to increased 1-year graft loss in the RYGB cohort (RYGB: 12.5% vs control: 3.1%, p 0.057).

*Conclusions: Despite the substantial weight loss attributed to BS in our population, patients with pre-TXP RYGB demonstrated increased rates of fungal infection after transplant and trended toward increased bacterial infection. While the anatomical complexity associated with LTX surgery after RYGB did not appear to significantly affect ICU or hospital length of stay, it likely contributed to overall infectious risk, and possibly to impaired graft survival. While rejection rates were not increased, arguing against RYGB associated impairment of immunosuppressive absorption, bypass of the host natural barrier defenses of the stomach could contribute to infectious risk in this population. Future larger scale studies to better explore risks associated with LTX after RYGB are needed, as the incidence of this procedure becomes increasingly more common in pre-TXP patients.

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