Bariatric Surgery: BMI Disputed as Key Eligibility Criterion

Larry Hand

October 22, 2013

Although body mass index (BMI) is often used as a threshold to determine eligibility for bariatric surgery, other factors such as age and type 2 diabetes status may be better predictors of 10-year mortality for obese individuals, according to an article published online October 16 in JAMA Surgery.

On the basis of their study of 15,394 obese patients included in the United Kingdom General Practice Research Database, Raj S. Padwal, MD, from the Department of Medicine, University of Alberta, Edmonton, Canada, and colleagues argue that BMI should no longer be used as the main eligibility criterion for bariatric surgery.

The authors included in their analysis patients aged 18 to 65 years who had a BMI of 35 kg/m2 or higher, as well as patients with a BMI of 30 to 34.9 kg/m2 who also had an obesity-related comorbidity, including hypertension, dyslipidemia, heart failure, type 2 diabetes, and cerebrovascular disease (CVD). The patients had an average BMI of 36.2 kg/m2, and they had become eligible for bariatric surgery between January 1 and December 31, 1998.

Using a binary logistic regression analysis, the researchers developed a clinical prediction rule for 10-year all-cause mortality. They found that a simple 4-variable prediction rule can be used to predict 10-year mortality in obese individuals eligible for bariatric surgery, with the 4 variables being age, sex, smoking, and diabetes. Although BMI was significantly related to mortality, its inclusion in the model did not improve its accuracy.

"Age, type 2 diabetes mellitus, male sex, smoking, BMI, coronary artery disease, and CVD were significant predictors of all-cause mortality, with age and diabetes having the largest impact," the researchers write.

Odds ratios for their final model turned out to be age, at 1.09 per year (95% confidence interval [CI], 1.07 - 1.10); type 2 diabetes, at 2.25 (95% CI, 1.76 - 2.87); current smoking, at 1.62 (95% CI, 1.28 - 2.06); and male sex, at 1.50 (95% CI, 1.20 - 1.87).

"Our results challenge conventional wisdom emphasizing the importance of BMI as a prognostic indicator for mortality in individuals eligible for bariatric surgery and, of equal import, the practice of using BMI as a surrogate for long-term prognosis," the researchers write.

This research follows closely other researchers' conclusions that BMI was not a strong predictor of diabetes remission after Roux-en-Y gastric bypass surgery.

The prediction rule the current researchers developed enables clinicians to calculate risk on the basis of individuals' characteristics, they write. Such individual quantification could be used to make decisions about allocating bariatric surgery procedures in environments "where large demand-supply gaps exist," they write.

"We know that BMI correlates at least to a degree with risk of surgery. The problem is that BMI doesn't accurately reflect adiposity," Scott Shikora, MD, director of the Center for Metabolic Health and Bariatric Surgery at Brigham and Women's Hospital, Boston, Massachusetts, told Medscape Medical News. He was not involved in the study.

That caveat aside, Dr. Shikora said he had a couple of concerns about the study. "The BMI mean was 36.2, and that's on the low side. That can skew the data. The average BMI of most bariatric programs is probably between 45 and 55, depending on if it's inner city or not," Dr. Shikora explained. "The all-cause mortality was 2.1%. That seems to me to be a bit high. Other than that, I think what the study is saying makes sense."

The authors note that a limitation of the study includes the possible lack of generalizability to a population outside the United Kingdom.

The researchers conclude, "[O]ur findings demonstrate that factors other than BMI are important in predicting the risk of death in patients eligible for bariatric surgery and that, of the obesity-related comorbidities, type 2 diabetes mellitus is the most important mortality predictor. Given that diabetes mellitus is highly amenable to surgical treatment, a strong case could be made for prioritizing it over BMI or other comorbidities."

This research was supported by the Canadian Institutes of Health Research. One coauthor has received honoraria from and has consulted for Ethicon Endo-Surgery, Covidien, and Gore, and one coauthor has received research funding from Johnson and Johnson and Ethicon Endo-Surgery and has consulted for Johnson and Johnson, Ethicon Endo-Surgery, Covidien, Bard, Baxter, and Olympus. The other authors have disclosed no relevant financial relationships.

JAMA Surg. Published online October 16, 2013. Abstract

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