Body mass index, or BMI, is a measurement that provides information about an individual's risk of health problems due to body fat composition. It is used in adults, children and teens to assess the possibility of weight problems. It is useful for doctors to identify children with weight problems so that healthy eating habits can be established early on.
Children
The American Academy of Pediatrics recommends the use of BMI measurements as a screening tool for weight-related health problems in children beginning at 2 years old. In contrast to adult BMI, the interpretation of a child's BMI measurements depends on age. The BMI-for-age growth charts are different for boys and girls. These take into account normal changes in BMI that occur during growth and development.
Calculation
To determine BMI, first measure the child's height and weight accurately. Calculate BMI by dividing the weight in pounds by height in inches squared and then multiply by a conversion factor of 703. When using the metric system, the formula for BMI is weight in kilograms divided by height in meters squared.
Interpretation
To interpret the results of BMI measurements in children, the value is plotted on the BMI-for-age growth charts to determine a percentile ranking. Children with BMI measurements that fall between the 5th and 85th percentile are considered of healthy weight. Those who fall below the 5th percentile are underweight. Children with a BMI between the 85th and 95th percentile are considered overweight and those in the 95th percentile or above are considered obese.
Considerations
BMI is not a perfect tool and should be interpreted in the context of overall health over time. For example, it is common for BMI to increase during puberty. Children with a large frame or with a great deal of muscle may have high BMI measurements even though they are at a healthy weight. Likewise a small-framed child might have too much body fat even though their BMI measurement places them in the normal range.
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