Obesity Ranking System Predicts Mortality

An obesity classification system that distinguishes between fat and lean tissue and takes into account functional status and the various comorbid conditions that can be associated with obesity may be a more effective mortality prediction tool than standard body mass index (BMI), according to new research....

Raj S. Padwal, MD, from the Department of Medicine, University of Alberta, Edmonton, Canada, explains, "Anthropometric-based classification schemes for excess adiposity do not include direct assessment of obesity-related comorbidity and functional status and thus have limited clinical utility." The new tool, called the Edmonton obesity staging system (EOSS), ranks obese and overweight people according to a 5-point scale based on factors relating to an individual's underlying health status and the presence or absence of underlying health conditions and, therefore, may be a better predictor of mortality.

A "0" on the EOSS scale, for instance, represents "no apparent risk factors (e.g., blood pressure, serum lipid and fasting glucose levels within normal range), physical symptoms, psychopathology, functional limitations and/or impairment of well-being related to obesity," according to the study authors.

A ranking of 2 indicates "the presence of established obesity-related chronic disease (e.g., hypertension, type 2 diabetes, sleep apnea, osteoarthritis), moderate limitations in activities of daily living and/or well-being," and the highest ranking indicates, "severe (potentially end-stage) disabilities from obesity-related chronic diseases, severe disabling psychopathology, severe functional limitations and/or severe impairment of well-being."

In determining efficacy of the tool, researchers with the University of Alberta applied it to data on 8143 people aged 20 years and older in the 1988-1994 and 1999-2004 US National Health and Human Nutrition Examination Surveys (NHANES).

The results indicated that 77.2% of overweight or obese people in the 1988-1994 survey and 90.3% of those in the 1999-2004 survey were classified as stage 1 or 2 in the EOSS, and their risk for death was significantly lower than that of overweight or obese people classified as stage 3.

In the NHANES 1988-1994 data, scores of 2 and 3 each were associated with a higher risk for dying (hazard ratio, 1.57; 95% confidence interval [CI], 1.16 - 2.13; hazard ratio, 2.69; 95% CI, 1.98 - 3.67, respectively) compared with scores 0 or 1.

The higher risk was seen even after adjustment for BMI, metabolic syndrome, and hypertriglyceridemic waist (i.e., waist circumference ≥ 90 cm and a triglyceride level ≥ 2 mmol/L for men or ≥ 85 cm and ≥ 1.5 mmol/L for women), as well as in a cohort eligible for bariatric surgery.

Measurements of BMI and waist circumference are typically among key factors in the assessment of appropriate treatments for obesity, such as bariatric surgery or anti-obesity therapies.

But BMI fails to directly distinguish between fat and lean tissue, and neither measurement reflects underlying obesity-related functional status or health conditions, which can include diabetes, hypertension, dyslipidemia, osteoarthritis, liver disease or kidney disease, or metabolic syndrome.

In considering the broader range of factors, the EOSS is intended to provide more clinically relevant prognostic information in a manner similar to that of the tumor, node, metastasis system used in the staging of cancer, the authors write.

"The major incremental contribution of this staging system to anthropometric indices and cardiovascular risk equations is the direct measurement of the presence and severity of underlying obesity-related comorbidities, which enables a more comprehensive and individualized assessment of risk," they said.

"Such enhanced risk assessment may enable a greater understanding of obesity-related prognosis and may also assist in determining the urgency of intervention."

The system could be particularly beneficial in prioritizing patients for bariatric surgery according to ranking that reflects a broader assessment of obesity and obesity-related comorbid conditions than simply a BMI ranking, the authors added.

Canadian Medical Association Journal, August 15, 2011 cmaj.110387