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SAN DIEGO -- It's common for kidney transplant centers to reject potential recipients because they are highly obese, but critics in recent years have called these standards too strict. Now, a new study of transplant outcomes suggests that these restrictions are "arbitrary and unfounded," because these patients can actually fare well compared with their non-obese counterparts.

"If carefully selected obese patients undergo transplant, their overall long-term patient outcomes are comparable among all transplant recipients with body mass index [BMI] above 30," said the study's lead author, Bhavna Chopra, MD, a transplant nephrologist at Allegheny General Hospital in Pittsburgh. "There is increased risk of delayed graft function with increasing BMI category. But [these patients] do OK once the kidney works."

The study findings were reported at ASN Kidney Week 2018, the annual meeting of the American Society of Nephrology (ASN).

Chopra noted that most kidney transplant centers won't allow procedures in patients with a BMI above 35 or 40: "This has been done primarily due to the known increased risk of surgical complications -- wound healing and delayed graft function," she said.

Research has suggested other obesity-related risks. For example, a of transplant outcomes found "significant benefits" for patients with BMI under 30 in mortality, acute rejection, delayed graft function, patient survival, and other measures.

But obese patients may still benefit from transplantation versus dialysis. Several reports have called on transplant centers to rethink their strict obesity cut-offs and take a wider variety of factors into account.

"Transplant-related decisions should be guided by medical considerations and the patients' best interests, regardless of their BMI," wrote the authors of a that analyzed access to kidney transplants in France. The authors of said "it's time to treat obesity as one risk factor among many others and not as an independent and additional hurdle for transplant listing."

For the new study, Chopra and colleagues examined United Network for Organ Sharing data regarding deceased kidney-only donors from 2006 to 2015. A total of 39,334 were tracked -- including 4,949 (13%) with BMI >35 -- for a median of 44 months. Graft failure occurred in 12% of recipients, and death in 11%.

Compared with patients with BMI >35, those in all the other BMI groups had a numerically higher risk of death:

• BMI 18-25: adjusted HR 1.08, P=0.08
• BMI >25-30: adjusted HR 1.04, P=0.30
• BMI >30-35: adjusted HR 1.06, P=0.20

The adjusted risk of graft failure and death-censored graft failure (dcGF) was lower in all these groups. The gap was widest, at an adjusted HR of 0.77, in the dcGF category for the 18-25 BMI group (P<0.001).

Compared with the risk in the >35 BMI group, the risk of delayed graft function was much lower in the lower-BMI groups (all P<0.001), as follows:

• BMI 18-25: OR 0.41
• BMI >25-30: OR 0.55
• BMI >30-35: OR 0.71

"Higher rates of dcGF among all patients with BMI >30 may reflect hyperfiltration, inflammation, subtherapeutic immunosuppression, or increased postoperative complications," Chopra and colleagues wrote. "Non-inferior patient outcomes among patients with BMI >35 could reflect careful pre-transplant selection among very obese candidates or a survival advantage similar to that of obese dialysis patients."

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