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A Simple Prediction Rule for All-Cause Mortality in Bariatric Surgery Eligible Patients



sharma-obesity-blood-sugar-testing2Regular readers will be quite familiar with our previous work on the Edmonton Obesity Staging System (EOSS), which ranks bariatric patients on a five-point ordinal scale based on the presence and severity of functional, mental and medical health problems.

As we showed in our analyses of several large datasets, individuals at higher EOSS stages are at far greater risk of all-cause mortality than individuals at lower EOSS stages. Interestingly enough, we found that BMI levels contribute little, if anything, to the actual mortality risk of these individuals – apparently, all that counts is how “sick” you are, not how “big” you are.

While EOSS is gradually winding its way around the globe towards greater popularity and acceptance, my colleagues and I now publish an even simpler rule for predicting all-cause mortality in bariatric patients – the paper was just released online at JAMA-Surgery.

In this paper, we studied over 15,000 individuals from the United Kingdom General Practice Research Database (GPRD), a population-representative primary care registry, who met current eligibility criteria for bariatric surgery (BMI, ≥35.0 alone or 30.0-34.9 with an obesity-related comorbidity) between January 1, 1988, through December 31, 1998.

We used binary logistic regression to construct a parsimonious model and a clinical prediction rule for 10-year all-cause mortality.

The final model, which included age, type 2 diabetes mellitus, current smoking, and male sex had a concordance or C-statistic of 0.768.

Based on this model, we developed a simply clinical prediction rule, scoring into 4 tiers with 10-year all-cause mortality ranging from was 0.2% in tier 1 to5.2% in tier 4.

Although BMI significantly (albeit poorly) predicted mortality, it did not add much to the model in terms of discrimination or calibration.

Thus, our findings show that all-cause 10-year mortality in obese individuals eligible for bariatric surgery can be estimated using a simple 4-variable prediction rule based on age, sex, smoking, and diabetes mellitus.

Once again (as in EOSS), body mass index was not an important mortality predictor.

These findings may have important consequences for prioritization of patients for bariatric surgery, at least if one chooses to prioritize individuals with the highest mortality risk – these would be older men with type 2 diabetes, who smoke (whereby, one would assume that they would immediately stop smoking if nothing else).

However, we also realize that mortality risk is only one consideration that goes into deciding who will benefit the most from surgery.

Certainly, severe obesity is associated with numerous other important consequences on mental, physical and economic health, which, although not lethal, can well make life quite unpleasant. The positive impact of bariatric surgery on these problems is well documented and probably as (if not more) important to people living with obesity than simply staying alive.

Nevertheless, to clinicians and administrators the message is clear – BMI alone is not a good predictor of health and certainly not a predictor of mortality. Prioritization systems based on BMI should be abandoned.

You can estimate your own 10-year all-cause mortality risk here.

@DrSharma
Montreal, QC

5 Comments

  1. I am underwhelmed by this metric as a useful tool for prioritizing surgery. Older smokers have been demonstrated to have higher mortality rates for surgery so if one concentrates on these patients then the rate of serious morbidity and mortality for bariatric surgery patients in your practice will rise. Further, the recidivism rate in smokers is generally high; and people who smoke after their gastric bypass have the most problems with anastomotic ulcers/strictures and heal the most poorly after any complication.

    I believe a better case could be made for concentrating on the young (<40?) diabetic patients with a low enough 'excess body weight' that when they undergo the expected amount of weight loss after surgery, they will have predictable resolution of their T2DM and other comorbidities. This cohort will predictably have the most to gain from their post-surgical benefit, will cost the system the least in the long run, and will likely be more productive and tax-paying members of society. They will spend a lot more time benefiting from the intervention, in other words.

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  2. My 90-year-old father will be delighted to learn that he has only a 5% chance of time in the next 10 years.

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  3. While your research may have shown that older, male smokers will have the greatest reduction in death over the following 10 years, it does not mean they will have the best outcomes from surgery.

    I understand we live in a society (Canadian) whereby we prioritize medical access based on many factors including who is the sickest. Yet, I would suggest that when it comes to all things bariatric, those who are the sickest may not benefit the most. As obesity is a progressive disease, I believe there is merit in treating those who may not be the most severe. Why do super, morbidly obese 20 somethings need to wait until they are old and sick to have the only viable treatment? Why wait until they can’t walk or until they are insulin dependent before they can access surgical intervention? Why wait until they have 40 or 50 years of weight bias and discrimination and mental health consequences when it can be addressed much earlier with hopefully a better chance at being “successful”.

    Of course someone who is an overweight/obese 60 year old smoker will have the highest reduction in 10 year mortality. They are already at such a risk that any intervention will achieve results.

    Let’s find a way to track the results of early treatment. Let’s see if we can make prevention work better!

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  4. Certainly, severe obesity is associated with numerous other important consequences on mental, physical and economic health, which, although not lethal, can well make life quite unpleasant. The positive impact of bariatric surgery on these problems is well documented and probably as (if not more) important to people living with obesity than simply staying alive. – See more at: http://www.drsharma.ca/a-simple-prediction-rule-for-all-cause-mortality-in-bariatric-surgery-eligible-patients.html#sthash.BbSHknql.dpuf

    You’re not wrong, but it makes me absolutely sick that we are addressing appearanced-based prejudice and discrimination (let’s be direct about what you’re talking about, here) by offering the victims a risky surgery meant to change their appearance. Weight discrimination is a very serious social justice issue, and few people take it seriously as such.

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