Sensitivity and specificity of body mass index as a definition of the obesity component of metabolic syndrome.

Metabolic syndrome (MS) is a combination of risk factors that are associated with several chronic diseases. Its components (obesity, dyslipidemia, carbohydrate intolerance, hypertension, microalbumineria) are diverse, whose thresholds vary in different definitions of MS. For example, a World Health Organization (WHO) panel defined the obesity component of MS based on waist-hip ratio, or body mass index (BMI), while the National Cholesterol Education Program (NCEP) defined the obesity component of MS by waist circumference. Since BMI is the common measure of obesity in most epidemiological studies, this research addressed how accurately the obesity component of MS is captured by BMI alone. Data presented showed that in a population with high prevalence of obesity, the specificity of detecting the obesity component of MS by BMI alone is almost 100%, but the sensitivity is low (e.g., < 50%). Individuals with high BMI generally have large waist-hip ratio and wide waist circumference, but the converse is not necessarily true. Consequently, centralized obesity (a risk factor for several chronic diseases) is not always captured by a high BMI alone.