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Bariatric surgery associated with long-term kidney function improvement

JAMA Network Open
Reuters Health - 10/09/2020 - People with obesity who undergo bariatric surgery may have better long-term kidney function than without weight-loss surgery, a new study suggests.

Researchers examined data on 144 adults with a BMI of 35 or higher who underwent bariatric surgery and were matched 1:1 to with a non-surgery cohort based on sex, self-reported race, preoperative BMI, age, and estimated glomerular filtration rate using creatinine.

In the surgery group, mean estimated glomerular filtration rate using creatinine declined 0.41 mL/min/1.73m2 over a mean follow-up of 9.2 years. In the non-surgical cohort, mean estimated glomerular filtration rate using creatinine declined 1.44 mL/min/1.73m2 over a mean follow-up of 8.2 years, according to the results in JAMA Network Open.

"Having impaired kidney function should not prevent a patient from having bariatric surgery, especially since they may have particularly positive benefits in terms of kidney function," said lead study author Dr. Alex Chang, a nephrologist and co-director of the Kidney Health Research Institute at Geisinger in Danville, Pennsylvania.

"Interestingly, patients who had lower kidney function appeared to have an even greater benefit of bariatric surgery in terms of their kidney function," Dr. Chang said by email.

The kidney benefit of bariatric surgery was similar when adjusted for baseline BMI and when measured using several other kidney filtration markers.

Some of the benefit is likely driven by improvements or resolution of diabetes and hypertension, Dr. Chang said.

With obesity, the large caloric, sodium, and protein load may overwork the kidneys, and imbalances of fat-related hormones could result in increased inflammation, and fat around the kidney can compress the kidney and trigger increased salt retention and higher blood pressure, Dr. Chang added.

"The large reduction in weight and caloric intake that occurs after bariatric surgery may reverse a lot of these effects," Dr. Chang said. "We plan on doing more research to better understand what changes in metabolism occur after bariatric surgery impact kidney function."

Other studies have found improvements in kidney health with sustained non-surgical weight loss as well, so all efforts should be made to help prevent and manage obesity, Dr. Chang noted.

With bariatric surgery, there are some potential risks such as nutritional deficiencies and kidney stones, so clinicians should ensure that patients undergo careful screening and shared decision-making with a multidisciplinary team, Dr. Chang added.

One limitation of the study was the requirement that patients survive the interval period to be included in the analysis. Another drawback is the potential for selection bias.

Impaired kidney function is not necessarily among the criteria for surgery, but most patients with hypertension, diabetes and severe obesity have some form of kidney impairment that might be improved as a secondary benefit of bariatric surgery, said Dr. Michel Gagner, a senior consultant at Hopital du Sacre Coeur in Montreal, and chief of surgery at Westmount Square Surgical Center.

"If there is documentation of kidney impairment, then there should be more pressure to have patients operated sooner to prevent permanent kidney damage, as we know that these patients may progress to need a kidney transplantation because of failure, later in life," Dr. Gagner, who wasn't involved in the study, said by email.

By Lisa Rapaport

SOURCE: https://bit.ly/3hdkEIA JAMA Network Open, online September 4, 2020.

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