A survey of pediatricians in North Carolinawhere the rate of overweight youth exceeds the national averageshowed that body mass index (BMI) charting prompted greater recognition of a weight problem than height and weight charting. Far more of the practitioners used charting of traditional height and weight data than charting of BMI to determine a child's overweight status, however.
Investigators issued the 356 participating pediatricians one of two survey instruments, both of which included a case vignette for a hypothetical 10-year-old African-American girl. One group of respondents received a version that provided the child's height; height percentile-for-age; weight; and weight percentile-for-age, as well as a Centers for Disease Control and Prevention (CDC) growth chart on which these data were plotted. The second group of respondents received the same child's BMI for a single time point and BMI percentile-for-age, along with the CDC growth chart with the BMI percentile-for-age plotted. Participants in both groups then were asked to respond to questions about the child's weight status and their level of concern about it, using a seven-point numeric scale. They also were queried about what methods they had been using in their practice to determine if a patient was overweight.
Respondents in the BMI group perceived the child as closer to the "too fat" extreme of the scale than did those in the height and weight group. Likewise, the BMI group was more concerned than the height and weight group about current and future medical and psychological consequences of overweight. Most often, respondents reported using weight and height charts concurrently to screen for overweight. Only 11% of providers reported "always" using BMI for this purpose, and a full 31% said they "never" used BMI when determining if a patient is overweight (Perrin EM et al: J Pediatr 2004;144:455).
Commentary: The height and weight of the sample patient were on the curves in traditional growth charts, but were disproportionate enough to give her an elevated BMI. The authors speculate that this is a common finding, increasing the importance of calculating BMI annually on all patients.
BMI is the weight in kilograms divided by the square of the height in meters. For those of us stuck in the English measurement system, an easy conversion is: BMI = (weight in pounds/height in inches squared) x 703. But the easiest method available is to use the calculator provided by the CDC at http://www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm .