Standardization of waist circumference reference data.

Studies continue to show that the measurement of waist circumference (WC) with the use of a tape measure enhances diagnostic sensitivity for risk factors relating to coronary artery disease, but most of the studies have focused on adults (1, 2). In this issue of the Journal, Esmaillzadeh et al (3) report that 75.9% of a sample of 3036 adolescents aged 10–19 y and living in Tehran, Iran, who had the hypertriglyceridemic waist (HW) phenotype were overweight and had a significantly higher prevalence of all metabolic risk factors except elevated fasting glucose than did adolescents with other phenotypes. The comparison of the HW phenotype, overweight, and metabolic syndrome with respect to the ability to predict the presence or absence of a risk factor showed that the HW phenotype has a significantly higher percentage of correct prediction than does overweight. Three key points can be summarized from this report. First, the results indicate that increasing WC in young persons has health risk factors similar to those in adults. This is important information because pediatric obesity is an increasingly global concern. Second, WC is equally useful in predicting health risk in persons as young as 10 y old as it is in adults. This additional characteristic of individual health risk classification could be of great value when it is interpreted together with other risk factors, such as serum triacylglycerol concentrations. The result provides additional evidence to support the routine measurement of WC in all patients in primary care. Third, WC and serum triacylglycerol concentrations are highly correlated in children of homogeneous background, but the relations could vary by racial-ethnic background or lifestyle. Therefore, caution is required in interpreting this study’s results for prognostic or diagnostic purpose in heterogeneous populations such as that of the United States. What may be of the greatest importance to the health care community is also the most critical requirement: standardization of WC reference data. Some attempts have been made over the past decade to generate standardized WC reference data (4, 5). However, those data sets do not include non-Western populations, and the International Committee on Standardization has endorsed none of these results. Until a serious and critical review of the currently available WC databases is completed, these values should be regarded as references rather than as medical tools. The most efficient way of solving this problem would be for the inquiry to be developed by 1 or 2 scientific leaders in conjunction with a scientific committee of epidemiologists, statisticians, and clinical scientists and practitioners who are interested in the topic and who can apply their experience to standardizing the inexpensive WC measurement as a useful tool in primary health care. The latest data from the National Health and Nutrition Examination Survey could be used as the basic database, and data from other countries could be considered. The existing databases for standardization have 2 advantages: they take less time, and their costs are lower. Concerns have arisen over the past few decades because WC has been measured at different locations by different groups of investigators, which could lead to different WC values. A previous study found that WC values measured at 4 commonly used locations were highly correlated (6). Thus, data obtained at different study sites with the use of these 4 commonly used measurement protocols could be pooled to increase the database for standardization process. Standardization of WC has been done for each sex separately. In general, sex determines body shape, such as the size of the chest, waist, or hips, whereas standardization of WC by age alone might not be applicable even in a homogenous population (4). For instance, a WC of 90 cm would be considered normal for tall men but would be considered a health-related concern for short men. Race or ethnicity also has a major effect on human body contour (7). Any differences in WC between racial-ethnic groups at any given age may not be proportional to the differences in average height between the study cohorts. The standardization of WC in relation to BMI has been suggested (5). Whether such an approach could yield less sensitive definitions of WC with regard to health risks or whether standardization of WC in relation to height and by sex and race-ethnicity would make WC a sensitive and specific tool for screening diseases could be evaluated with standard statistical tests using available databases. The unit for standardization is just as important as the definition of standardization. Therefore, one should select a term or a unit for WC standardization that investigators will accept logically and mathematically and that would increase the use of WC measurement in the clinical field. The percentile system has been used for decades to evaluate children’s rate of growth in terms of weight and height (8), and the T-score system has been used to interpret bone density measurement for screening fracture risk (9). Views on the issue abound, but nearly everyone would agree that not enough well-documented information is available to justify an endorsement of either of the 2 terms. This would be an