Using the CDC BMI-for-age Growth Charts to Assess Growth in the United States Among Children and Teens Aged 2 to 20 Years
The Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) recommend that health care providers in primary care settings use the 2000 CDC growth reference charts for children and teens aged 2 to 20 years to monitor growth in the United States (Grummer-Strawn, Reinold, Krebs, 2010).
The 2000 CDC growth reference charts include the weight-for-age, stature-for-age, and BMI-for-age charts for boys and girls aged 2 to 20 years. This training focuses on using the BMI-for-age growth charts.
What is BMI?
- An anthropometric index of weight and height
Body Mass Index (BMI) is a calculated measure of weight relative to height, defined as body weight in kilograms divided by height in meters squared (Keys et al., 1972).
BMI = weight (kg) / height (m)2
- A screening tool
BMI is a screening tool used to identify individuals who have underweight, healthy weight, overweight, or obesity. BMI alone is NOT intended to be used as a diagnostic tool (Barlow, 2007).
For example, a child who has excess weight relative to height might have a high BMI for his or her sex and age. To determine whether the child has excess weight for health or associated health risks, further assessment is needed, as recommended by the American Academy of Pediatrics [PDF-359KB].
For children and teens, BMI is both sex-specific and age-specific (Barlow, 2007; Hammer et al., 1991; Pietrobelli et al., 1998). Age and sex are taken into consideration for children and teens for two reasons: during typical healthy growth, (1) the amount and distribution of body fat differs between girls and boys; and (2) the amount of body fat changes with age.
- An indirect measure of adiposity
BMI is not a direct measure of adiposity (body fatness). However, BMI parallels direct measures of adipose tissue, such as those obtained by dual energy X-ray absorptiometry (DEXA). Higher BMIs are more strongly associated with higher adiposity and cardiovascular risk factors.
Note that the accuracy of BMI as an indicator of adiposity varies depending on the degree of adiposity. In other words, among relatively heavy children, BMI is a good indicator of excess body fatness; however, among children with a healthy weight (a BMI-for-age > 5th and < 85th percentile), BMI is more an indicator of fat-free mass (Freedman and Sherry, 2009). Fat-free mass is total body mass excluding the fat. Fat-free mass includes everything from your skin, bones, ligaments, and tendons, to your organs and water content.